Interfacing Peripherals To Computer System Or Disk Interfacing Technology

Interfacing Peripherals to Computer System

Conceived By-

Shubham Pandey Department of Electronics Engineering A.I.E.T Lucknow, Uttar Pradesh India

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Disclaimer

The work followed is original editing of mine (but the information has been referred through many internet sources) and has been conceived as the part of the seminar report submitted to the institution. This is to therefore kindly inform the viewers that any information in this report should not be trusted blindly and thus I am not responsible for any ill consequences arising due to this.

Shubham Pandey Azad Institute of Engineering and Technology Lucknow, Uttar Pradesh, India

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Disk Interface Technology

The demand for storage to be available anytime, anywhere is driving the development of a new mix of disk interface technologies. This guide provides a basic comparison of existing and emerging technologies to help sort through the options that are available today and in the future. A comparative matrix of key features follows.

Parallel Advanced Technology Attachments (ATA) Parallel ATA, commonly referred to as simply ―ATA‖, is an industry specification that evolved from the original Advanced Technology disk-interface. The ATA standard, first developed in 1984 defines a command and register set for the interface between the disk drive and the PC. Today’s ATA-133 interface delivers a maximum data transfer rate of 133 MB/sec and supports two parallel ports, with each port supporting two internal hard drives. ATA is currently the standard hard disk drive interconnect in desktop PCs and is implemented in many Direct Attached Storage (DAS) and Network Attached Storage (NAS) systems.

Parallel Small Computer System Interface (SCSI) Parallel SCSI, better known as ―SCSI‖, is a shared bus technology that connects various internal and external devices to a PC or server. SCSI technology allows for connectivity of up to 15 devices, and Ultra320 SCSI supports a data transfer rate of up to 320 MB/sec. First approved as a standard in 1986, SCSI technology has evolved to be the most widely used interface in workstations, as well as in servers and networked storage systems today.

Fiber Channel (FC) Fiber Channel serves two purposes. It is both a high-speed switched fabric technology, and a disk interface technology. It supports a maximum data transfer rate of 400 MB/sec (full duplex; or half duplex, dual loop configuration) over 30 meters of copper cable or 10 kilometers over single-mode fiber optic links. When implemented in a continuous arbitrated loop (FC-AL), Fiber Channel can support up to 127 individual storage devices and host systems without a switch. Disk arrays and backup devices directly attach to the loop rather than onto any one server. FC was first approved as a standard in 1994 and is primarily implemented in high-end SAN systems.

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Serial Advanced Technology Attachments 1.0 (SATA) Developed in 2001, SATA is the first generation of the new disk interface technology replacing Parallel ATA. In desktops, SATA is expected to replace Parallel ATA as the primary internal storage for PCs. SATA 1.0 delivers a maximum data transfer rate of 1.5 GB/sec (1500 MB/sec) per port and its future roadmap shows growth to 6.0 GB/sec (6000 MB/sec). Advantages of SATA include a point-to-point interconnect that enables full bandwidth available to each device, lower pin-count, lower voltage, hot-plug capability, thin cabling, longer cable length and register-level compatibility with Parallel ATA. These added features make SATA an option for DAS, NAS and some Storage Area Network (SAN) systems where Parallel ATA may not have been considered.

Serial Advanced Technology Attachments II (SATA II) SATA II is the second-generation SATA disk interface technology currently under development by the SATA working group. The SATA II specification picks up where SATA 1.0 left off, and will be deployed in 2 phases. The first phase, called ―Extensions to Serial ATA 1.0‖, focuses primarily on addressing the needs of servers and networked storage. These include queuing, enclosure services, hot plug, cold presence detect, cabling and backplane improvements. The second phase is anticipated to scale performance to 3.0 GB/sec (3000 MB/sec) per port. These combined enhancements will make SATA II a good option for DAS, NAS and SAN storage systems where price/performance and cost are key factors.

Serial Attached Small Computer System Interface (SAS) Serial Attached SCSI (SAS) is under development by the T10 standards committee. This committee is addressing the future limitations of the parallel SCSI interface, principally the bandwidth scaling limitations inherent in a parallel interface. SAS will deliver a maximum data transfer of 3.0 GB/sec (3000 MB/sec) per device, and it can support up to 128 devices via an expander. One of the key features of SAS is its anticipated ability to allow users to connect either a SATA or a SAS hard disk drive in an enclosure with expander capabilities. Its point-to-point configuration and highly scalable architecture makes SAS a good option for mid-range to high-end DAS, NAS and SAN storage systems.

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ATA

Performance Technology 2000 Introduction (Year)

SCSI

Fiber Channel

SATA

SATA II

Serial Attached SCSI

2002

2001

2002

2003

2004

Maximum Bus Speed

100 MB/s shared per channel

320 MB/s Shared per channel

4 GB/s dedicated or shared

1.5GB/sec dedicated per device

3 GB/sec dedicated per device

3 GB/sec dedicated per device

Topology

Shared bus Shared bus master/slave

Point-topoint

Point-topoint

Point-topoint

Number of Device /Channel

2

15

Arbitrated loop/ switched fabric 127/ arbitrated loop

1 1 (expandable (expandable to 128) to 128)

1 (expandable to 128)

Command Queuing

No

Yes

Yes

Yes

Yes

Yes

Internal /External

External

Internal

Internal /External

Internal /External

Enterprise

Enterprise

Few

Desktop with some Enterprise features Many

Enterprise

Many

Desktop with some Enterprise features Many

1.75 inches

0.156 inches

0.312 inches

0.312 inches

0.312 inches

68 or 80

4

22 (7 signal)

22 (7 signal)

22 (7 signal)

12 metres

10 Kms

1 metres

6 metres

10 metres

Primary Applications Internal Device Placement Desktop Hard Disk Drive(HDD) Classes Devices other than HDDs

Many

Characteristics 2 inches Internal cable width Number of cable pins Maximum Cable length [Type text]

40 (+40 conductors) 18 inches

Few

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Parallel Advanced Technology Attachments (PATA) ATA/ATAPI is an evolution of the AT Attachment Interface, which was itself evolved in several stages from Western Digital's original Integrated Drive Electronics (IDE) interface. Parallel ATA (PATA) is an interface standard for the connection of storage devices such as hard disks, solid-state drives, and CD-ROM drives in computers. The standard is maintained by X3/INCITS committee. It uses the underlying AT Attachment and AT Attachment Packet Interface (ATA/ATAPI) standards. Parallel ATA only allows cable lengths up to 18 in (460 mm). Because of this length limit the technology normally appears as an internal computer storage interface. The name of the standard was originally conceived as "PC/AT Attachment" as its primary feature was a direct connection to the 16-bit ISA bus introduced with the IBM PC/AT. The name was shortened to "AT Attachment" to avoid possible trademark issues. It is not spelled out as "Advanced Technology" anywhere in current or recent versions of the specification; it is simply "AT Attachment". IDE and ATA-1 The term Integrated Drive Electronics (IDE) refers not just to the connector and interface definition, but also to the fact that the drive controller is integrated into the drive, as opposed to a separate controller on or connected to the motherboard. The integrated controller presented the drive to the host computer as an array of 512-byte blocks with a relatively simple command interface. This relieved the software in the host computer of the chores of stepping the disk head arm, moving the head arm in and out, and so on, as had to be done with earlier ST-506 and ESDI hard drives. All of these low-level details of the mechanical operation of the drive were now handled by the controller on the drive itself. This also eliminated the need to design a single controller that could handle many different types of drives, since the controller could be unique for the drive. The host need only ask for a particular sector, or block, to be read or written, and either accept the data from the drive or send the data to it. The second ATA interface Originally, there was only one ATA controller in early PCs, which could support up to two hard drives. At the time in combination with the floppy drive, this was sufficient for most people, [Type text]

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and eventually it became common to have two hard drives installed. When the CDROM was developed, many computers were unable to accept them due to already having two hard drives installed. Adding the CDROM would have required removal of one of the drives. Although SCSI was available as a CDROM expansion option at the time, but devices with SCSI were more expensive than ATA devices due to the need for a smart controller that is capable of bus arbitration. SCSI typically added US$ 100-300 to the cost of a storage device, in addition to the cost of a SCSI controller. The less-expensive solution was the addition of the second ATA interface, typically included as an expansion option on a sound card. It was included on the sound card because early business PCs did not include support for more than simple beeps from the internal speaker, and tuneful sound playback was considered unnecessary for early business software. ATA ruled as the primary storage device interface and in some systems a third and fourth motherboard interface was provided for up to eight ATA devices attached to the motherboard. Enhanced IDE (EIDE) included most of the features of the forthcoming ATA-2 specification and several additional enhancements. Other manufacturers introduced their own variations of ATA-1 such as "Fast ATA" and "Fast ATA-2". ATA-2 also was the first to note that devices other than hard drives could be attached to the interface. AT Attachments Packet Interface (ATAPI) The introduction of ATAPI (ATA Packet Interface) by a group called the Small Form Factor committee allowed ATA to be used for a variety of other devices that require functions beyond those necessary for hard disks. ATAPI devices include CD-ROM and DVD-ROM drives, tape drives, and large-capacity floppy drives such as the Zip drive and Super Disk drive. ATAPI is actually a protocol allowing the ATA interface to carry SCSI commands and responses; therefore all ATAPI devices are actually "speaking SCSI" other than at the electrical interface. In fact, some early ATAPI devices were simply SCSI devices with an ATA/ATAPI to SCSI protocol converter added on. The SCSI commands and responses are embedded in "packets" (hence "ATA Packet Interface") for transmission on the ATA cable. This allows any device class for which a SCSI command set has been defined to be interfaced via ATA/ATAPI. Drive size limitations The original ATA specification used a 28-bit addressing mode, allowing for the addressing of 228 sectors of 512 bytes each, resulting in a maximum capacity of about 137 GB. The BIOS in early PCs imposed smaller limits such as 8.46 GB, with a maximum of 1024 cylinders, 256 heads and 63 sectors, but this was not a limit imposed by the ATA interface. ATA-6 introduced 48-bit [Type text]

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addressing, increasing the limit to 144 Petabytes. As a consequence, any ATA drive of capacity larger than 137 gigabytes must be an ATA-6 or later drive. Connecting such a drive to a host with an ATA-5 or earlier interface will limit the usable capacity to the maximum of the controller.

Parallel ATA interface Parallel ATA cables transfer data 16 bits at a time. ATA's ribbon cables have had 40 wires for most of its history (44 conductors for the smaller form-factor version used for 2.5" drives), but an 80 wire version appeared with the introduction of the Ultra DMA/33 (UDMA) mode. All of the additional wires in the new cable are ground wires, interleaved with the previously defined wires to reduce the effects of capacitive coupling between neighboring signal wires, reducing crosstalk. Capacitive coupling is more of a problem at higher transfer rates, and this change was necessary to enable the 66 MB/s transfer rate of UDMA4 to work reliably. The faster UDMA5 and UDMA6 modes also require 80-conductor cables. Connector Assignments and Color Coding: For the first time, the 80-conductor cable defines specific roles for each of the connectors on the cable; the older cable did not. Color coding of the connectors is used to make it easier to determine which connector goes with each device: Blue: The blue connector attaches to the host (motherboard or controller). Gray: The gray connector is in the middle of the cable, and goes to any slave (device 1) drive if present on the channel. Black: The black connector is at the opposite end from the host connector and goes to the master drive (device 0), or a single drive if only one is used.

(PATA connector cable side)

Pin

Signal

Description

1

/RESET

Reset

2

GND

Ground

3

DD7

Data 7

4

DD8

Data 8

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5

DD6

Data 6

6

DD9

Data 9

7

DD5

Data 5

8

DD10

Data 10

9

DD4

Data 4

10 DD11

Data 11

11 DD3

Data 3

12 DD12

Data 12

13 DD2

Data 2

14 DD13

Data 13

15 DD1

Data 1

16 DD14

Data 14

17 DD0

Data 0

18 DD15

Data 15

19 GND

Ground

20 KEY

Key

21 n/c

Not connected

22 GND

Ground

23 /IOW

Write Strobe

24 GND

Ground

25 /IOR

Read Strobe

26 GND

Ground

27 IO_CH_RDY

I/O channel ready

28 ALE

Address Latch Enable

29 n/c

Not connected

30 GND

Ground

31 IRQR

Interrupt Request

32 /IOCS16

IO Chip Select 16

33 DA1

Address 1

must be designated as device 0 (commonly

34 n/c

Not connected

referred to as master) and the other as device 1

35 DA0

Address 0

36 DA2

Address 2

37 /IDE_CS0

(1F0-1F7)

drives to share the cable without conflict. The

38 /IDE_CS1

(3F6-3F7)

master drive is the drive that usually appears

39 /ACTIVE

Led driver

"first" to the computer's BIOS and/or operating

40 GND

Ground

system. The mode that a drive must use is often set

(Comparison between the size of 40 conductor cable)

(40 conductor PATA Cable)

Multiple devices on a cable If two devices attach to a single cable, one

(slave). This distinction is necessary to allow both

by a jumper setting on the drive itself, which must be manually set to master or slave. If there is a single device on a cable, it should be configured as master Cable Select [Type text]

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Cable select is controlled by pin 28. The host adapter grounds this pin; if a device sees that the pin is grounded, it becomes the master device; if it sees that pin 28 is open, the device becomes the slave device. This setting is usually chosen by a jumper setting on the drive called "cable select", usually marked CS, which is separate from the "master" or "slave" setting. Note that if two drives are configured as master and slave manually, this configuration does not need to correspond to their position on the cable. Pin 28 is only used to let the drives know their position on the cable; it is not used by the host when communicating with the drives. With the 40-wire cable it was very common to implement cable select by simply cutting the pin 28 wire between the two device connectors; putting the slave device at the end of the cable, and the master on the middle connector. If there is just one device on the cable, this results in an unused stub of cable, which is undesirable for physical convenience and electrical reasons. The stub causes signal reflections, particularly at higher transfer rates. Starting with the 80-wire cable defined for use in ATAPI5/UDMA4, the master device goes at the end of the 18-inch (460 mm) cable--the black connector--and the slave device goes on the middle connector--the gray one--and the blue connector goes onto the motherboard. So, if there is only one (master) device on the cable, there is no cable stub to cause reflections. Two devices on one cable — speed impact It is a common misconception that, if two devices of different speed capabilities are on the same cable, both devices' data transfers will be constrained to the speed of the slower device. For all modern ATA host adapters this is not true, as modern ATA host adapters support independent device timing. This allows each device on the cable to transfer data at its own best speed. Only one device on a cable can perform a read or write operation at one time, therefore a fast device on the same cable as a slow device under heavy use will find it has to wait for the slow device to complete its task first. However, most modern devices will report write operations as complete once the data is stored in its onboard cache memory, before the data is written to the (slow) magnetic storage. This allows commands to be sent to the other device on the cable, reducing the impact of the "one operation at a time" limit. Parallel AT version details and features ATA-1 (IDE), 8.3MBytes/sec, 8 or 16 bit data width, 40 pin data ribbon cable/connector. With a maximum of 2 devices on the bus. Using PIO Modes 0, 1 or 2. Performed no bus [Type text]

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error correction. The ATA-1 specification was released in 1994, and was withdrawn in 1999. ATA-2 (EIDE, or Fast ATA), 16.6MBytes/sec, 8 or 16 bit data width, 40 pin data ribbon cable/connector. With a maximum of 4 devices on the bus. Using PIO Modes 0, 1, 2, 3, or 4. The ATA-2 specification was released in 1995 and was withdrawn in 2001. ATA-3, 16MBytes/sec, 16 bit data width, 40 pin data ribbon cable/connector. Using PIO Modes 0, 1, 2, 3, or 4 and Multiword DMA modes 1 and 2. Runs with 120nS Strobes (rising edge to rising edge). Includes CRC. ATAPI (ATA Packet Interface) is the CD-ROM side of the interface. It uses the same connector as ATA, and adds 1 for analog and 1 for digital audio. The ATA-3 specification was released in 1997 and was withdrawn in 2002. ATA-4 Ultra-ATA/33, 33MBytes/sec, 16 bit data width, 40 pin data ribbon cable/connector. Using PIO Modes 0, 1, 2, 3, or 4 and Multiword DMA modes 1 and 2 and Ultra DMA modes 0, 1, and 2. Runs with 120 nS strobes (rising edge to rising edge), but used both edges of the Strobe producing an effective 60nS Strobe rate. 33MBps Transfer speed = [(1/120nS) x 2 bytes x 2]. Where 120nS cycle time is 4 clock periods at 30nS each. Added CRC checking. The ATA-4 standard was released in 1998. ATA-5 Ultra-ATA/66, 66MBytes/sec, 16 bit data width 40 pin data connector/80 pin cable, with the additional 40 new pins being Ground. The new cable allows ATA/66 to run at a faster rate then ATA/33. Using PIO Modes 0, 1, 2, 3, or 4 and Multiword DMA modes 1 and 2 and Ultra DMA modes 0, 1, 2, 3 and 4. Runs with 60nS Strobes (rising edge to rising edge), but uses both edges of the Strobe producing an effective 30nS Strobe rate. 66MBps Transfer speed = [(1/60nS) x 2 bytes x 2]. Where 60nS cycle time is 2 clock periods at 30nS each. The ATA-5 standard was released in 2000. ATA-6 Ultra-ATA/100, 100MBytes/sec,16 bit data width 40 pin data connector/80 pin cable, with the additional 40 new pins being Ground. Using PIO Modes 0, 1, 2, 3, or 4 and Multiword DMA modes 1 and 2 and Ultra DMA modes 0, 1, 2, 3, 4 and 5. 100MBps Transfer speed = [(1/40nS) x 2 bytes x 2]. Where 40nS cycle time is 2 clock periods at 20nS each. The ATA-6 standard was released in 2002. ATA-7 Ultra-ATA/133, 133MBytes/sec,16 bit data width 40 pin data connector/80 pin cable, with the additional 40 new pins being Ground. Using PIO Modes 0, 1, 2, 3, or 4 and Multiword DMA modes 0, 1 and 2 and Ultra DMA modes 0, 1, 2, 3, 4, 5 and 6. 133MBps Transfer speed = [(1/30nS) x 2 bytes x 2]. Where 30nS cycle time is 2 clock periods at 15nS each. The ATA-7 standard was released in 2005. With the introduction of Serial ATA, this is the last expected update of the IDE [PATA] bus. SATA is faster, and requires a smaller cable, which means better air flow in the case. [Type text]

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Parallel Small Computer System Interface SCSI is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it can connect a wide range of other devices, including scanners and CD drives. The SCSI standard defines command sets for specific peripheral device types; the presence of "unknown" as one of these types means that in theory it can be used as an interface to almost any device, but the standard is highly pragmatic and addressed toward commercial requirements. SCSI is an intelligent interface: it hides the complexity of physical format. Every device attaches to the SCSI bus in a similar manner. SCSI is a peripheral interface: up to 8 or 16 devices can be attached to a single bus. There can be any number of hosts and peripheral devices but there should be at least one host. SCSI is a buffered interface: it uses hand shake signals between devices, SCSI-1, SCSI-2 have the option of parity error checking. Starting with SCSI-U160 (part of SCSI-3) all commands and data are error checked by a CRC32 checksum. SCSI is a peer to peer interface: the SCSI protocol defines communication from host to host, host to a peripheral device, peripheral device to a peripheral device. However most peripheral devices are exclusively SCSI targets, incapable of acting as SCSI initiators unable to initiate SCSI transactions themselves. Therefore peripheral-to-peripheral communications are uncommon, but possible in most SCSI applications. An overview

SCSI Type SCSI-1 SCSI-2 SCSI-2 fast/wide SCSI-3 SCSI-3 fast/wide

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Speed (MBps) 1 to 5

Bus Width 8

Pins

5 to 10 up to 40

8 16

50 50

8

16 32

68 68

32

25 or 50

ID's 8

8

32

Connector Sub-D25, Amphenol 50, Sub-D50 Micro-D50 Micro-D50 Micro-D68 Micro-D68

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The SCSI interface is a parallel interface the communication between devices is done by initiators and targets. An initiator is a device which requests something from a target. The initiator is most commonly a host-adapter in a computer. The target is the one that takes the job and carries it out. Because of the definition of SCSI that a job is given by a initiator and then carried out by a target without the initiator knowing how the target is doing it and even not knowing when the job is done the roles of initiator and target may switch. As soon as the target is done with its job it initiates the host, which will become target. The purpose of all this is that as soon as the target knows what the initiator wants the bus will become free for other jobs to be send to other targets. The bus is used more economically. Instead of a computer waiting for data coming from a scanner, the bus can be used by the computer to read data from the hard disk. SCSI has the capability to connect more than two devices to a bus. These devices may be targets or initiators. So it is possible for two hosts to share one tape streamer, but it is also possible for one host to have access to several hard disks. The identification of the devices is done by an ID. SCSI-1 and SCSI-2 have a maximum of 8 ID's and SCSI-3 has even 32 possible ID's. There is no such thing as plain SCSI. There is SCSI-1, -2 and -3 and together with this there is Differential and Single-ended, and for the termination there is passive and active. Single-ended means that there is a ground and a signal wire. Much like in RS232. Differential on the other hand has no ground wire, but all signals have two wires, a positive and a negative one and the voltage difference between them carries the information (1 or 0). Much like RS422. To make everything more complex the SCSI bus must be terminated to work properly. In SCSI there is active termination, which means the termination is done by a voltage regulator and some resistors. This is for the Single-Ended interface. With differential SCSI live is easier. There is only passive termination which means a resistor is placed at the end and at the beginning of the cable. But it's not the same termination as for passive single-ended SCSI. And finally there is the difference between SCSI-3 and SCSI-2 wide. Both have 16 bytes transmissions, but SCSI-2 has only 50 wires and SCSI-3 has 68, so why take a, more expensive cable? The reason is that SCSI-2 has a 50 wire cable and only 8 data lines there will be a low and high byte transmission. Each 16 bit word is split in a low and a high byte. These are transmitted one after the other and thus taking twice as long as 16 bit SCSI-3. This makes SCSI-3 faster and more economic. There are a dozen SCSI interface names, most with ambiguous wording (like Fast SCSI, Fast Wide SCSI, Ultra SCSI, and Ultra Wide SCSI); three SCSI standards, each of which has a collection of modular, optional features; several different connector types; and three different types of voltage signaling. The leading SCSI card manufacturer, Adaptec, has manufactured over 100 varieties of SCSI cards over the years. In actual practice, many experienced technicians simply refer to SCSI devices by their bus bandwidth (i.e. SCSI 320 or SCSI 160) in Megabytes per second. [Type text]

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SCSI-1 features an 8-bit parallel bus (with parity), running asynchronously at 3.5 MB/s or 5 MB/s in synchronous mode, and a maximum bus cable length of 6 meters. A rarely seen variation on the original standard included a high-voltage differential (HVD) implementation whose maximum cable length was 25 meters. SCSI-2 standard was introduced in 1994 and gave rise to the Fast SCSI and Wide SCSI variants. Fast SCSI doubled the maximum transfer rate to 10 MB/s and Wide SCSI doubled the bus width to 16 bits on top of that to reach a maximum transfer rate of 20 MB/s. Ultra-2 SCSI was introduced in 1997 and featured a low-voltage differential (LVD) bus. For this reason ultra-2 is sometimes referred to as LVD SCSI. LVD's greater resistance to noise allowed a maximum bus cable length of 12 meters. At the same time, the data transfer rate was increased to 80 MB/s. Ultra-2 SCSI actually had a relatively short lifespan, as it was soon superseded by Ultra-3 (Ultra-160) SCSI. Ultra-3 also known as Ultra-160 SCSI and introduced toward the end of 1999, this version was basically an improvement on the ultra-2 standard, in that the transfer rate was doubled once more to 160 MB/s by the use of double transition clocking. Ultra-160 SCSI offered new features like cyclic redundancy check (CRC), an error correcting process, and domain validation. Ultra-320 is the Ultra-160 standard with the data transfer rate doubled to 320 MB/s. The latest working draft for this standard is revision 10 and is dated May 6, 2002. Nearly all SCSI hard drives being manufactured at the end of 2003 were Ultra-320 devices. Ultra-640, otherwise known as Fast-320 was promulgated as a standard (INCITS 367-2003 or SPI5) in early 2003. Ultra-640 doubles the interface speed yet again, this time to 640 MB/s. Ultra-640 pushes the limits of LVD signaling; the speed limits cable lengths drastically, making it impractical for more than one or two devices. Because of this, most manufacturers have skipped over Ultra640 and are developing for Serial Attached SCSI instead. SCSI IDs All devices on a parallel SCSI bus must have a SCSI ID. The initiator (adapter or controller) SCSI ID is usually set by a physical jumper or switch. The target (disk-drive) SCSI IDs are either set by physical jumpers or by control signals which vary for each connector on an enclosure backplane. The SCSI ID field widths are: Bus-width ID width IDs available [Type text]

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8-bit 16-bit

3-bit 4-bit

8 16

Arbitration All SCSI commands start with a process called arbitration when one or more devices attempt to access the bus. During the arbitration phase, the 8 or 16 data bus signals are used to identify which device(s) are requesting access. All SCSI devices must implement the same arbitration algorithm so the result is always unanimous. SCSI IDs are used in the arbitration phase to determine which device next gets access to the SCSI bus. If two devices attempt to access the bus at the same time then the one with the highest priority SCSI ID will win the arbitration. The priority sequence for an 8-bit wide parallel SCSI bus is quite simple, but the priority sequence for a 16-bit wide parallel SCSI bus has to meet legacy requirements so is less obvious: Bus width SCSI ID priority (from highest to lowest) 8-bit

7, 6, 5, 4, 3, 2, 1, 0

16-bit

7, 6, 5, 4, 3, 2, 1, 0, 15, 14, 13, 12, 11, 10, 9, 8

The SCSI ID of the initiator is usually set to the highest priority value of 7. If there are two initiators then their SCSI IDs are usually set to 7 and 6. All the remaining SCSI IDs can then be used for disk-drives or other target devices. The arbitration process can use up a lot of bus bandwidth so more recent devices support a simplified protocol called Quick Arbitration and Selection (QAS). Termination Parallel SCSI buses must always be terminated at both ends to ensure reliable operation. Without termination, data transitions would reflect back from the ends of the bus causing pulse distortion and potential data loss. A positive DC termination voltage is provided by one or more devices on the bus, typically the initiator(s). This positive voltage is called TERMPOWER and is usually around +4.3 volts. TERMPOWER is normally generated by a diode connection to +5.0 volts. This is called a diode-OR circuit, designed to prevent backflow of current to the supplying device. A device that supplies TERMPOWER must be able to provide up to 900 mA (single-ended SCSI) or 600 mA (differential SCSI).

[Type text]

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Termination can be passive or active. Passive termination means that each signal line is terminated by two resistors, 220 Ω to TERMPOWER and 330 Ω to ground. Active termination means that there is a small voltage regulator which provides a +3.3 V supply. Each signal line is then terminated by a 110 Ω resistor to the +3.3 V supply. Active termination provides a better impedance match than passive termination because most flat ribbon cables have a characteristic impedance of approximately 110 Ω. Forced perfect (FPT) termination is similar to active termination, but with added diode clamp circuits which absorb any residual voltage overshoot or undershoot. There is a special case in SCSI systems that have mixed 8-bit and 16-bit devices where high-byte termination may be required. In current practice most parallel SCSI buses are LVD and so require external, active termination. The usual termination circuit consists of a +3.3 V linear regulator and commercially available SCSI resistor network devices. Pin configuration of 50 pin SCSI Pin #

Single Ended Signal Name

Differential Signal Name

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

GROUND GROUND GROUND GROUND GROUND GROUND GROUND GROUND GROUND GROUND GROUND RESERVED OPEN RESERVED GROUND GROUND GROUND GROUND GROUND

GROUND +DB0 +DB1 +DB2 +DB3 +DB4 +DB5 +DB6 +DB7 +PARITY DIFFSENSE RESERVED TERMPWR RESERVED +ATN GROUND +BSY +ACK +RST

[Type text]

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20 21 22 23 24 25

GROUND GROUND GROUND GROUND GROUND GROUND

+MSG +SEL +C/D +REQ +I/O GROUND

Pin #

Single Ended Signal Name

Differential Signal Name

26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

-DB0 -DB1 -DB2 -DB3 -DB4 -DB5 -DB6 -DB7 -PARITY GROUND GROUND RESERVED TERMPWR RESERVED GROUND -ATN GROUND -BSY -ACK -RST -MSG -SEL -C/D -REQ -I/O

GROUND -DB0 -DB1 -DB2 -DB3 -DB4 -DB5 -DB6 -DB7 -PARITY GROUND RESERVED TERMPWR RESERVED -ATN GROUND -BSY -ACK -RST -MSG -SEL -C/D -REQ -I/O GROUND

Pin configuration of 68 pin SCSI Pin # 1 2 3 4 5 6 7 8 9 10 11 12 13

Single Ended Signal Name GROUND GROUND GROUND GROUND GROUND GROUND GROUND GROUND GROUND GROUND GROUND GROUND GROUND

[Type text]

Differential Signal name +DB12 +DB13 +DB14 +DB15 +PARITY1 GROUND +DB0 +DB1 +DB2 +DB3 +DB4 +DB5 +DB6 Page 17

14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

GROUND GROUND GROUND TERMPWR TERMPWR RESERVED GROUND GROUND GROUND GROUND GROUND GROUND GROUND GROUND GROUND GROUND GROUND GROUND GROUND GROUND GROUND

+DB7 +PARITY DIFFSENSE TERMPWR TERMPWR RESERVED +ATN GROUND +BSY +ACK +RST +MSG +SEL +C/D +REQ +I/O GROUND +DB8 +DB9 +DB10 +DB11

Pin # Single Ended Signal Name 35 -DB12 36 -DB13 37 -DB14 38 -DB15 39 -PARITY1 40 -DB0 41 -DB1 42 -DB2 43 -DB3 44 -DB4 45 -DB5 46 -DB6 47 -DB7 48 -PARITY 49 GROUND 50 GROUND 51 TERMPWR 52 TERMPWR 53 RESERVED 54 GROUND 55 -ATN 56 GROUND 57 -BSY 58 -ACK 59 -RST 60 -MSG 61 -SEL 62 -C/D 63 -REQ 64 -I/O 65 -DB8 66 -DB9 67 -DB10 68 -DB11

Differential Signal name -DB12 -DB13 -DB14 -DB15 -PARITY1 GROUND -DB0 -DB1 -DB2 -DB3 -DB4 -DB5 -DB6 -DB7 -PARITY GROUND TERMPWR TERMPWR RESERVED -ATN GROUND -BSY -ACK -RST -MSG -SEL -C/D -REQ -I/O GROUND -DB8 -DB9 -DB10 -DB11

Fibre Channel

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FC is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 - INCITS. It started use primarily in the supercomputer field, but has become the standard connection type for SAN in enterprise storage. Despite its name, Fibre Channel signaling can run on both twisted pair copper wire and fiber-optic cables. Fibre Channel deploys Fibre Channel Protocol (FCP) which predominantly transports SCSI commands over Fibre Channel networks. Fibre Channel topologies There are three major Fibre Channel topologies, describing how a number of ports are connected together. A port in Fibre Channel terminology is any entity that actively communicates over the network, not necessarily a hardware port. This port is usually implemented in a device such as disk storage, an HBA on a server or a Fibre Channel switch. 1) Point-to-Point (FC-P2P). Two devices are connected back to back. This is the simplest topology, with limited connectivity. 2) Arbitrated loop (FC-AL). In this design, all devices are in a loop or ring, similar to token ring networking. Adding or removing a device from the loop causes all activity on the loop to be interrupted. The failure of one device causes a break in the ring. Fibre Channel hubs exist to connect multiple devices together and may bypass failed ports. A loop may also be made by cabling each port to the next in a ring. A minimal loop containing only two ports, while appearing to be similar to FC-P2P, differs considerably in terms of the protocol. Multiple pairs of ports may communicate simultaneously in a loop. 3) Switched fabric (FC-SW). All devices or loops of devices are connected to Fibre Channel switches, similar conceptually to modern Ethernet implementations. Advantages of this topology over FC-P2P or FC-AL include: The switches manage the state of the fabric, providing optimized interconnections. The traffic between two ports flows through the switches only, it is not transmitted to any other port. Failure of a port is isolated and should not affect operation of other ports.

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Optical carrier medium variants Media Type

Speed (MByte/s)

Transmitter

Distance

Single-Mode Fiber

400

1300 nm Long wave Laser

2 m - 2 km

200

1550 nm Long wave Laser 1300 nm Long wave Laser 1550 nm Long wave Laser 1300 nm Long wave Laser 1300 nm Long wave Laser 850 nm Short wave Laser

2 m - >50 km 2 m - 2 km 2 m - >50 km 2 m - 10 km 2 m - 2 km 0.5 m - 150m

100

Multimode Fiber (50µm)

400 200 100

0.5 m - 300m 0.5 m - 500m 2 m - 175m

Fibre Channel and Networks Though it has many features of a network, Fibre Channel is less a network than a high speed switching system that interconnects relatively local devices. With its high bandwidth and ability to support multiple protocols simultaneously, Fibre Channel enables near-instant access to massive amounts of data in SANs and other modern computing environments. Collision-based Ethernet networks are ubiquitous, largely because they allow multiple individual clients to share retrieved data in a very simple and economical way. Such networks are most successful when supporting front-end functions. However, they are too inefficient to be used in block-level storage environments, such as those found in data centers. For throughput, scalability, and attainable network lengths, Fibre Channel is far superior to Ethernet. Data throughput With the currently available 2Gb-rated Fibre Channel in the network, data transfer rates are very close to 200MB/s, as expected. In a Gigabit Ethernet network, however, collision management claims so much bandwidth that even 1Gb rates are difficult to achieve consistently. Scalability. Whether device connections consist of a single point-to-point link or involve hundreds of integrated, enterprise wide servers, Fibre Channel networks perform with equal reliability, high rates, and flexible configuration, achieving scalable densities up to thousands of ports. Although IP-based storage networks theoretically can scale to hundreds of ports, there is no widespread use to demonstrate this capability. Network lengths. With Fibre Channel, the switches and cables that carry the data, can be either copper or optical fibre. Performance is the same, though copper is limited in length to less than 3 meters. Without the benefit of repeaters, long-haul copper Ethernet networks are [Type text]

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limited to 100–200 meters, depending on the Ethernet protocol version. Currently, the maximum theoretical distance for long-haul Fibre Channel networks using fibre-optic links is 10 Kms. Deployment Scenarios of FC Workgroup SAN Consider this type of deployment when you need to manage many large files and rapidly growing amounts of data—video and audio editing and storage, for example. The RAID storage pool allows quick, reliable scaling of storage and backup capabilities. Fibre Channel uniquely provides in-order delivery of data, necessary for efficient access to media files. In addition to the Fibre Channel switch, dedicated metadata controllers help mediate traffic for maximum data transfer rates.

Fibre Channel connector pin configurations There are various Fibre Channel connectors in use in the computer industry. The following sections describe the most common Fibre Channel pinouts with some comments about the purpose of their electrical signals. The most familiar Fibre Channel connectors are cable connectors, used for interconnects between initiators and targets (usually disk enclosures). There are also "device connectors" that can be found on Fibre Channel disk-drives and backplanes of enclosures. The device connectors include pins for power and for setting disk options.

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9-pin "DE-9" cable connector Optional pins 2, 3, 7, and 8 are intended Pin Signal name Comments 1 +OUT Fibre channel output for use with an external optical 2 +5V Optional converter. This is often called a Media 3 Module Fault Detect Optional 4 Reserved Interface Assembly (MIA). Fibre 5 +IN Fibre channel input channel DE-9 connectors often have 6 -OUT Fibre channel output 7 Output Disable Optional only the 4 required contacts installed. 8 GND Optional, return for pin 2 Note that they are the four outermost 9 -IN Fibre channel input contacts. This is an easy way to tell a fibre channel cable from an RS-232 cable.

8-pin "HSSDC" cable connector (High Speed Serial Data Connection) Pin 1 2 3 4 5 6 7 8

Signal name +OUT GND -OUT Module Fault Detect Output Disable -IN +5V +IN

Comments Fibre channel output Optional, return for pin 7 Fibre channel output Optional Optional Fibre channel input Optional Fibre channel input

Optional pins 2, 4, 5, and 7 are intended for use with an external optical converter. This is often called a Media Interface Assembly (MIA).

40-pin "SCA-2" disk connector Although SCA-2 is the official name for this connector, it is often called SCA-40 to distinguish it by its pin count from other similar connectors. Pin Signal name

Comments

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Output driven high when port 1 is operating correctly

-EN Bypass Port 1 +12V +12V +12V -Parallel ESI -Drive Present ACTLED Power Control START1 START2 -EN Bypass Port 2 SEL6 SEL5 SEL4 SEL3 FLTLED DEVCTRL2 DEVCTRL1

[Type text]

Input to allow ESI operation using the SELx pins Output to drive the activity LED cathode Input to control spin-up behavior (see the Disk options section) Input to control spin-up behavior (see the Disk options section) Output driven high when port 2 is operating correctly Device ID bit 6 / ESI write clock Device ID bit 5 / ESI read clock Device ID bit 4 / ESI acknowledge clock Device ID bit 3 / ESI bit 3 Output to drive the fault LED cathode Input to control interface speed (see the Disk options section) Input to control interface speed (see the Disk options section) Page 22

19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

+5V +5V +12V Charge GND (12V) GND (12V) +IN1 -IN1 GND (12V) +IN2 -IN2 GND (12V) +OUT1 -OUT1 GND (5V) +OUT2 -OUT2 GND (5V) SEL2 SEL1 SEL0 DEVCTRL0 +5V CHARGE

Fibre channel input Fibre channel input Fibre channel input Fibre channel input Fibre channel output Fibre channel output Fibre channel output Fibre channel output Device ID bit 2 / ESI bit 2 Device ID bit 1 / ESI bit 1 Device ID bit 0 / ESI bit 0 Input to control interface speed (see the Disk options section)

Fibre Channel connectors

Fibre Channel connection port to computer

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Serial AT Attachments Serial ATA or simply SATA is the hard disk standard created to replace the parallel ATA interface, also known as IDE. SATA provides a transfer rate of 150 MB/s or 300 MB/s against of a 133 MB/s maximum using the previous technology. The conventional IDE port (now called parallel ATA or simply PATA) transfers data in parallel. The advantage of parallel transmission over serial transmission is the higher speed of the former mode, seeing that several bits are sent at the same time. Its major disadvantage, however, relates to noise. As many wires have to be used (at least one for each bit to be sent per turn), one wire generates interference in another. This is why ATA-66 and higher hard disks require a special, 80-wire cable. The difference between this 80-wire cable and the normal 40-wire IDE cable is that it includes a ground wire between each original wire, providing anti-interference shielding. Serial ATA, on the other hand, transmits data in serial mode, i.e. one bit per time. Traditional thinking makes us to think that serial transmission is slower than parallel transmission. This is only true if we are comparing transmissions using the same clock rate. In this case parallel transmission will be at least eight times faster, as it transmits at least eight bits (one byte) per clock cycle, compared to serial transmission where only one bit is transmitted per clock cycle. However, if a higher clock rate is used on serial transmission, it can be faster than parallel. That’s exactly what happens with Serial ATA. The problem in increasing parallel transmission transfer rate is increasing the clock rate, as the higher the clock rate, more problems with electromagnetic interference show up. Since serial transmission uses just one wire to transmit data it has fewer problems with noise, allowing it to use very high clock rates, achieving a higher transfer rate. Serial ATA standard transfer rate is of 1,500 Mbps. As it uses 8B/10B coding where each group of eight bits is coded into a 10-bit number, its effective clock rate is of 150 MB/s. Serial ATA devices running at this standard speed are also known as SATA-150. Serial ATA II provides new features such as Native Command Queuing (NCQ), plus a higher speed rate of 300 MB/s. Devices that can run at this speed are called SATA-300. The next standard to be released will be SATA-600. It is important to notice that SATA II and SATA-300 are not synonyms. One can build a device that runs only at 150 MB/s but using new features provided by SATA II such as NCQ. This device would be a SATA II device, even though it doesn’t run at 300 MB/s. NCQ increases the hard disk drive performance by reordering the commands send by the computer. It is also very important to notice that Serial ATA implements two separated data paths, one for transmitting and another for receiving data. On parallel design only one data path is available, which is shared for both data transmission and reception. Serial ATA cable consists in two pair of [Type text]

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wires (one for transmission and the other for reception) using differential transmission. Three ground wires are also used, so Serial ATA cable has seven wires. Another advantage of using serial transmission is that fewer wires need to be used. Parallel IDE ports use a 40-pin connector and 80wire flat cables. Serial ATA ports use a seven-pin connector and seven-wire cable. This helps a lot on the thermal side of the computer, as using thinner cables makes air to flow easier inside the PC case.

Features Hotplug

All SATA devices support hotplugging. However, proper hotplug

support requires the device be running in its native command mode not via IDE emulation, which requires AHCI. Some of the earliest SATA host adapters were not capable of this and furthermore some popular Operating Systems, such as Windows XP, still do not support AHCI. Advanced Host Controller Interface

As their standard interface, SATA controllers

use the Advanced Host Controller Interface, allowing advanced features of SATA such as hotplug and NCQ. If AHCI is not enabled by the motherboard and chipset, SATA controllers typically operate in "IDE emulation" mode which does not allow features of devices to be accessed if the ATA/IDE standard does not support them. Windows device drivers that are labeled as SATA are usually running in IDE emulation mode unless they explicitly state that they are AHCI. While the drivers included with Windows XP do not support AHCI, AHCI has been implemented by proprietary device drivers. Windows Vista, FreeBSD, Linux with kernel version 2.6.19 onward, as well as Solaris and OpenSolaris have native support for AHCI. Throughput

The current SATA specifications detail data transfer rates as high as

6 GBits/s per device. SATA uses only 4 signal lines cables are more compact and cheaper than PATA. SATA supports hot-swapping and NCQ.

Evolution SATA 1.5 (First generation)

First-generation SATA interfaces, now known as

SATA 1.5 communicates at a rate of 1.5 GBits/s. Taking 8b/10b encoding overhead into account, they have an actual encoded transfer rate of 1.2 GBits/s. The theoretical burst throughput of SATA 1.5 is similar to that of PATA/133, but newer SATA devices offer enhancements such as NCQ which improve performance in a multitasking environment. However, high-performance flash drives can transfer data at up to 201 MB/s, SATA 1.5 does not provide sufficient throughput for these drives. During the initial period after SATA [Type text]

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1.5 finalization, adapter and drive manufacturers used a "bridge chip" to convert existing PATA designs for use with the SATA interface. Bridged drives have a SATA connector, may include either or both kinds of power connectors, and generally perform identically to their PATA equivalents. Most lack support for some SATA-specific features such as NCQ. Bridged products gradually gave way to native SATA products.

SATA 3 GBits/s (Second generation)

Soon after the introduction of SATA 1.5Gbit/s,

a number of shortcomings emerged. At the application level SATA could handle only one pending transaction at a time like PATA. The SCSI interface has long been able to accept multiple outstanding requests and service them in the order which minimizes response time. This feature, NCQ, was adopted as an optional supported feature for SATA 1.5 GBit/s and SATA 3 GBit/s devices. First-generation SATA devices operated at best a little faster than parallel ATA/133 devices. Subsequently, a 3 GBit/s signaling rate was added to the physical layer (PHY layer), effectively doubling maximum data throughput from 150 MB/s to 300 MB/s. For mechanical hard drives, SATA 3 GBit/s transfer rate is expected to satisfy drive throughput requirements for sometime, as the fastest mechanical drives barely saturate a SATA 1.5 GBit/s link. A SATA data cable rated for 1.5 GBit/s will handle current mechanical drives without any loss of sustained and burst data transfer performance. However, high-performance flash drives are approaching SATA 3 GBit/s transfer rate. Given the importance of backward compatibility between SATA 1.5 GBit/s controllers and SATA 3 GBit/s devices, SATA 3 GBit/s auto-negotiation sequence is designed to fall back to SATA 1.5 GBit/s speed when in communication with such devices. In practice, some older SATA controllers do not properly implement SATA speed negotiation. Affected systems require the user to set the SATA 3 GBit/s peripherals to 1.5 GBit/s mode, generally through the use of a jumper, however some drives lack this jumper. Chipsets known to have this fault include the VIA VT8237 and VT8237R Southbridge, and the VIA VT6420, VT6421A and VT6421L standalone SATA controllers. SiS's 760 and 964 chipsets also initially exhibited this problem, though it can be rectified with an updated SATA controller ROM. SATA II (committee renamed SATA-IO)

Popular usage refers to the SATA 3 Gbit/s

specification as Serial ATA II (SATA II or SATA2), contrary to the wishes of the Serial ATA International Organization (SATA-IO) which defines the standard. SATA II was originally the name of a committee defining updated SATA standards, of which the 3 Gbit/s standard was just one.

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SATA 6 GBits/s (Third generation)

Serial

ATA

International

Organization

presented the draft specification of SATA 6 GBit/s physical layer and ratified its physical layer specification in 2008. The full 3.0 standard was released in 2009. While even the fastest conventional hard disk drives can barely saturate the original SATA 1.5 GBit/s bandwidth, Solid State Disk drives are close to saturating the SATA 3 Gbit/s limit at 250 MB/s net read speed. Ten channels of fast flash can actually reach well over 500 MB/s with new ONFI drives, so a move from SATA 3 Gbit/s to SATA 6 Gbit/s would benefit the flash read speeds. As for the standard hard disks, the reads from their built-in DRAM cache will end up faster across the new interface. The new specification contains the following changes: o A new NCQ streaming command to enable Isochronous data transfers for bandwidth-hungry audio and video applications. o An NCQ Management feature that helps optimize performance by enabling host processing and management of outstanding NCQ commands. o Improved power management capabilities. o A small Low Insertion Force (LIF) connector for more compact 1.8-inch storage devices. o A connector designed to accommodate 7 mm optical disk drives for thinner and lighter notebooks. o Alignment with the INCITS ATA8-ACS standard. The enhancements are generally aimed at improving quality of service for video streaming and high priority interrupts. In addition, the standard continues to support distances up to a meter. The new speeds may require higher power consumption for supporting chips, factors that new process technologies and power management techniques are expected to mitigate. The new specification can use existing SATA cables and connectors, although some OEMs are expected to upgrade host connectors for the higher speeds. Also, the new standard is backwards compatible with SATA 3 Gbit/s. In order to avoid parallels to the common SATA II misnomer, the SATA-IO has compiled a set of marketing guidelines for the new specification. The specification should be called Serial ATA International Organization: Serial ATA Revision 3.0, and the technology itself is to be referred to as SATA 6 GBit/s. A product using this standard should be called the SATA 6 Gbit/s.

Cables and connectors Connectors and cables present the most visible differences between SATA and PATA drives. Unlike PATA, the same connectors are used on 3.5" SATA hard disks for desktop and server computers and 2.5" disks for portable or small computers, this allows 2.5" drives to be used in [Type text]

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desktop computers with only a mounting bracket and no wiring adapter. There is a special connector (eSATA) specified for external devices, and an optionally implemented provision for clips to hold internal connectors firmly in place. SATA drives may be plugged into SAS controllers and communicate on the same physical cable as native SAS disks, but SATA controllers cannot handle SAS disks.

Serial ATA Data Connector Pin 1 2 3 4 5 6 7

Function Ground A+ AGround BB+ Ground

The SATA standard defines a data cable with seven conductors (3 grounds and 4 active data lines in two pairs) and 8 mm wide wafer connectors on each end. SATA cables can have lengths up to 1 metre (3.3 ft), and connect one motherboard socket to one hard drive. SATA connectors and cables are easier to fit in closed spaces and reduce obstructions to air cooling. They are more susceptible to accidental unplugging and breakage than PATA, but

cables can be purchased that have a locking feature, whereby a small spring holds the plug in the socket. Designers use a number of techniques to reduce the undesirable effects of such unintentional coupling. One such technique used in SATA links is differential signaling. Serial ATA Power Connector Pin 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Function +3.3 V +3.3 V +3.3 V Ground Ground Ground +5 V +5 V +5 V Ground Reserved/Ground Ground +12 V +12 V +12 V

The SATA standard specifies a different power connector than the decades-old four-pin Molex connector found on pre-SATA devices. Like the data cable, it is wafer-based, but its wider 15-pin shape prevents accidental mis-identification and forced insertion of the wrong connector type. Native SATA devices favor the SATA power-connector, although some early SATA drives retained older 4-pin Molex in addition to the SATA power connector. Adapters exist which can convert a 4-pin Molex connector to a SATA power connector. However, because the 4-pin Molex connectors do not provide 3.3 V power, these adapters provide only 5 V and 12 V power and leave the 3.3 V lines unconnected. This precludes the use of such adapters with drives that require 3.3 V power.

SATA features more pins than the traditional power connector for several reasons: A third voltage is supplied, 3.3 V, in addition to the traditional 5 V and 12 V. [Type text]

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Each voltage transmits through three pins ganged together, because the small contacts by themselves cannot supply sufficient current for some devices. (Each pin should be able to provide 1.5 A.) Five pins ganged together provide ground. For each of the three voltages, one of the three pins serves for hotplugging. The ground pins and power pins 3, 7, and 13 are longer on the plug (located on the SATA device) so they will connect first. A special hot-plug receptacle (on the cable or a backplane) can connect ground pins 4 and 12 first. Pin 11 can function for staggered spinup, activity indication, or nothing. Staggered spinup is used to prevent many drives from spinning up simultaneously, as this may draw too much power. Activity is an indication of whether the drive is busy, and is intended to give feedback to the user through a LED. Topology SATA uses a point-to-point architecture. The connection between the controller and the storage device is direct. Modern PC systems usually have a SATA controller on the motherboard, or installed in a PCI or PCI Express slot. Most SATA controllers have multiple SATA ports and can be connected to multiple storage devices. There are also port expanders or multipliers which allow multiple storage devices to be connected to a single SATA controller port. Encoding These high-speed transmission protocols use a logic encoding known as 8b/10b encoding. The signal uses non-return to zero (NRZ) encoding with LVDS. In the 8b/10b encoding the data sequence includes the synchronizing signal. This technique is known as clock data recovery, because it does not use a separate synchronizing signal. Instead, it uses the serial signal's 0 to 1 transitions to recover the clock signal. Backward and forward compatibility SATA and PATA At the device level, SATA and PATA (Parallel Advanced Technology Attachment) devices remain completely incompatible they cannot be interconnected. At the application level, SATA devices can be specified to look and act like PATA devices. Many motherboards offer a "legacy mode" option which makes SATA drives appear to the OS like PATA drives on a standard controller. This eases OS installation by not requiring a specific driver to be loaded during setup [Type text]

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but sacrifices support for some features of SATA and generally disables some of the boards' PATA or SATA ports since the standard PATA controller interface only supports 4 drives. The common heritage of the ATA command set has enabled the proliferation of low-cost PATA to SATA bridge-chips. Bridge-chips were widely used on PATA drives (before the completion of native SATA drives) as well as stand-alone "dongles." When attached to a PATA drive, a device-side dongle allows the PATA drive to function as a SATA drive. Host-side dongles allow a motherboard PATA port to function as a SATA host port. The market has produced powered enclosures for both PATA and SATA drives which interface to the PC through USB, Firewire or eSATA, with the restrictions noted above. PCI cards with a SATA connector exist that allow SATA drives to connect to legacy systems without SATA connectors. SATA 1.5 Gbit/s and SATA 3 Gbit/s The designers of SATA aimed for backward and forward compatibility with future revisions of the SATA standard. According to the hard drive manufacturer Maxtor, motherboard host controllers using the VIA and SIS chipsets VT8237, VT8237R, VT6420, VT6421L, SIS760, SIS964 found on the ECS 755-A2 manufactured in 2003, do not support SATA 3 Gbit/s drives. Additionally, these host controllers do not support SATA 3 Gbit/s optical disc drives. To address interoperability problems, the largest hard drive manufacturer, Seagate/Maxtor, has added a user-accessible jumper-switch known as the Force 150, to switch between 150 MB/s and 300 MB/s operation. Users with a SATA 1.5 Gbit/s motherboard with one of the listed chipsets should either buy an ordinary SATA 1.5 Gbit/s hard disk, buy a SATA 3 Gbit/s hard disk with the user-accessible jumper, or buy a PCI or PCI-E card to add full SATA 3 Gbit/s capability and compatibility. Western Digital uses a jumper setting called OPT1 Enabled to force 150 MB/s data transfer speed. OPT1 is used by putting the jumper on pins 5 & 6. Comparisons with other interfaces SATA and SCSI SCSI currently offers transfer rates higher than SATA, but it uses a more complex bus, usually resulting in higher manufacturing costs. SCSI buses also allow connection of several drives (using multiple channels, 7 or 15 on each channel), whereas SATA allows one drive per channel, unless using a port multiplier. SATA 3 Gbit/s offers a maximum bandwidth of 300 MB/s per device compared to SCSI with a maximum of 320 MB/s. Also, SCSI drives provide greater sustained throughput than [Type text]

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SATA drives because of disconnect-reconnect and aggregating performance. SATA devices generally link compatibly to SAS enclosures and adapters, while SCSI devices cannot be directly connected to a SATA bus. SCSI, SAS and fibre-channel (FC) drives are typically more expensive so they are traditionally used in servers and disk arrays where the added cost is justifiable. Inexpensive ATA and SATA drives evolved in the home-computer market, hence there is a view that they are less reliable. As those two worlds overlapped, the subject of reliability became somewhat controversial. Note that, generally, the failure rate of a disk drive is related to the quality of its heads, platters and supporting manufacturing processes, not to its interface. SATA in comparison to other buses

Name

Raw bandwidth (MBit/s)

Transfer speed (MB/s)

Max. cable length (m)

Power provided

eSATA

3,000

300

2 with eSATA HBA (1 with passive adapter)

No

SATA 300

3,000

300

1

No

SATA 150 PATA 133

1,500 1,064

150 133

1 0.46 (18 in)

No No

SAS 300

3,000

300

8

No

SAS 150

1,500

150

8

No

3,144

393

786

98.25

393

49.13

5,000 480

625 60

100; alternate cables 15 W, 12– available for >100 m 25 V 15 W, 12– 100 25 V 15 W, 12– 4.5 25 V 3 4.5 W, 5 V 5 2.5 W, 5 V

2,560

320

12

No

10,520

2,000

2–50,000

No

126 (16,777,216 with switches)

No

126 (16,777,216 with switches)

No

1 with point to point Many with switched fabric

FireWire 3200 FireWire 800 FireWire 400 USB 3.0 USB 2.0 Ultra-320 SCSI Fibre Channel over optic fiber Fibre Channel over copper cable

4,000

InfiniBand 12× Quad- 120,000 rate

[Type text]

400

12 5 (copper)

12,000

<10,000 (fiber)

Devices Channel

per

1 (15 with multiplier) 1 (15 with multiplier) 1 per line 2 1 (16k expanders) 1 (16k expanders)

port port

with with

63 (with hub) 63 (with hub) 63 (with hub) 127 (with hub) 127 (with hub) 15 (plus the HBA)

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Port Multiplier Port Multiplier is a device that expands the number of devices to be installed on a single SATA port. Port multiplier has several applications, like allowing a home user to install more than one hard. Using port multiplier it is possible to connect them using fewer cables. For example, one port multiplier connected to one SATA port allows you to connect up to 15 hard disk drives to it. And you would have only one cable connecting the rack to the server. But there is a huge performance issue here. If a SATA-150 port were used, the 150 MB/s bandwidth would have to be split between 15 devices, creating a huge bottleneck. To solve this issue another approach may be used. Instead of using only one port multiplier chip, you could use four of them, connecting the rack to the server using four cables (instead of 16). The maximum transfer rate between the server and the rack would be of 600 MB/s (4x 150 MB/s) if SATA-150 ports were used or of 1,200 MB/s (4x 300 MB/s) if SATA-300 were used. Inside the rack, you could install up to 60 hard disk drives (15 x 4), but for optimal performance you should install four hard disk drives to each port multiplier chip, matching your 16 drives.

Block to explain Multi port HDD SATA

SATA Power Cable

Port Multiplier Card

eSATA and SATA cable

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Serial Attached SCSI A typical Serial Attached SCSI system consists of the following basic components: 1. Initiator: a device that originates device-service and task-management requests for processing by a target device and receives responses for the same requests from other target devices. Initiators may be provided as an on-board component on the motherboard (as is the case with many server-oriented motherboards) or as an add-on host bus adapter. 2. Target: a device containing logical units and target ports that receives device service and task management requests for processing and sends responses for the same requests to initiator devices. A target device could be a hard disk or a disk array system. 3. Service Delivery Subsystem: the part of an I/O system that transmits information between an initiator and a target. Typically cables connecting an initiator and target with or without expanders and backplanes constitute a service delivery subsystem. 4. Expanders: devices that form part of a service delivery subsystem and facilitate communication between SAS devices. Expanders facilitate the connection of multiple SAS End devices to a single initiator port. SAS v/s Parallel SCSI The SAS bus operates point-to-point while the SCSI bus is multidrop. Each SAS device is connected by a dedicated link to the initiator, unless an expander is used. If one initiator is connected to one target, there is no opportunity for contention, with parallel SCSI, even this situation could cause contention. SAS has no termination issues and does not require terminator packs like parallel SCSI. SAS eliminates clock skew. SAS supports up to 16,384 devices through the use of expanders, while Parallel SCSI has a limit of 8 or 16 devices on a single channel. SAS supports a higher transfer speed (3 or 6 GBit/s) than most parallel SCSI standards. SAS achieves these speeds on each initiator-target connection, hence getting higher throughput, whereas parallel SCSI shares the speed across the entire multidrop bus. SAS controllers may support connecting to SATA devices, either directly connected using native SATA protocol or through SAS expanders using SATA Tunneled Protocol (STP). Both SAS and parallel SCSI use the SCSI command-set.

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SAS v/s SATA Systems identify SATA devices by their port number connected to the host bus adapter, while SAS devices are uniquely identified by their World Wide Name (WWN). SAS protocol supports multiple initiators in a SAS domain, while SATA has no analogous provision. Most SAS drives provide tagged command queuing, while most newer SATA drives provide native command queuing, each of which has its pros and cons. SATA follows the ATA command set and thus only supports hard drives and CD/DVD drives. In theory, SAS also supports numerous other devices including scanners and printers. However, this advantage could also be moot, as most such devices have also found alternative paths via such buses as USB, IEEE 1394 (FireWire), and Ethernet. SAS hardware allows multipath I/O to devices while SATA (prior to SATA 3Gb/s) does not. Per specification, SATA 3Gb/s makes use of port multipliers to achieve port expansion. Some port multiplier manufacturers have implemented multipath I/O using port multiplier hardware. SATA is marketed as a general-purpose successor to parallel ATA and has become common in the consumer market, whereas the more-expensive SAS targets critical server applications. SAS error-recovery and error-reporting use SCSI commands which have more functionality than the ATA SMART commands used by SATA drives. SAS uses higher signaling voltages (800-1600 mV TX, 275-1600 mV RX) than SATA (400-600 mV TX, 325-600 mV RX). The higher voltage offers (among other features) the ability to use SAS in server backplanes. Because of its higher signaling voltages, SAS can use cables up to 8 m (26 ft) long, SATA has a cable-length limit of 1 m (3 ft). SAS Protocols SAS uses a few protocols to deal with a few different type of traffic flowing through it. It is worth mentioning them here because they are used a lot in talking about SAS. SSP stands for ―Serial SCSI Protocol‖ which encapsulates "legacy" SCSI commands and data for transmission between nodes. For example, if node "x" sends node "y" a command to "read data block 54", and node "y" sends back the data from that disk block, this transaction is done with SSP, which encapsulates the SCSI Command Block (CDB), the data, the "sense data" (error data, if [Type text]

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needed), and other basic information which is used in any SCSI transaction, parallel, serial, legacy, whatever. SMP stands for "SAS Management Protocol". It is used only by expanders and initiators (hosts). SMP provides a set of very simple commands to allow initiators and expanders to query information from each other. This is only done at start-up, or when a devices is added or removed from the bus. SMP is used to allow the initiator/host to discover what devices are on the SAS bus, so it may assign SCSI IDs to them and present them to the host. It is also used to allow the expanders to see what devices (WWNs) are connected off which ports of other expanders, so they will know how to open routes to different devices/WWNs. This sharing of information between initiators and expanders whenever the bus is new or changed, is called "discovery". It is simply, everyone asking their neighbors about who their neighbors are and collecting everyone’s addresses so ,for example, expanders will know through which port messages to different addresses should be routed. STP stands for "SAS Tunneling Protocol". This is simply the mechanism that a SAS topology uses to talk to, and route commands from/to SATA (Serial-ATA) devices. SATA devices use a wire level signaling that it somewhat similar to SAS, but outside of that, are quite different. SATA devices can be connected to a SAS topology however, and STP is used to tunnel this different data from a host, through the SAS network, to a SATA device. Architecture

SAS architecture consists of six layers: Physical layer: o

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defines electrical and physical characteristics Page 35

o

differential signaling transmission

o

Three connector types: 

SFF 8482 – SATA compatible



SFF 8484 – up to four devices



SFF 8470 – external connector (InfiniBand connector), up to four devices

PHY Layer: o

8b/10b data encoding

o

Link initialization, speed negotiation and reset sequences

o

Link capabilities negotiation (SAS-2)

Link layer: o

Insertion and deletion of primitives for clock-speed disparity matching

o

Primitive encoding

o

Data scrambling for reduced EMI

o

Establish and tear down native connections between SAS targets and initiators

o

Establish and tear down tunneled connections between SAS initiators and SATA targets connected to SAS expanders

o

Power management (proposed for SAS-2.1)

Port layer: o

Combining multiple PHYs with the same addresses into wide ports

Transport layer: o

Supports three transport protocols: 

Serial SCSI Protocol (SSP): supports SAS devices



Serial ATA Tunneled Protocol (STP): supports SATA devices attached to SAS expanders



Serial Management Protocol (SMP): provides for the configuration of SAS expanders

Application layer SAS Expanders The components known as Serial Attached SCSI Expanders (SAS Expanders) facilitate communication between large numbers of SAS devices. Expanders contain two or more external expander-ports. Each expander device contains at least one SAS Management Protocol target port for management and may contain SAS devices itself. For example, an expander may include a

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Serial SCSI Protocol target port for access to a peripheral device. There are two different types of expander: Edge Expanders and Fanout Expanders. An edge expander allows for communication with up to 128 SAS addresses, allowing the SAS initiator to communicate with these additional devices. Edge expanders can do direct table routing and subtractive routing. Without a fanout expander, we can use at most two edge expanders in our delivery subsystem A fanout expander can connect up to 128 sets of edge expanders, known as an edge expander device set, allowing for even more SAS devices to be addressed. The subtractive routing port of each edge expanders will be connected to the phys of fanout expander. A fanout expander can not do subtractive routing, it can only forward subtractive routing requests to the connected edge expanders. Connectors The SAS connector is much smaller than traditional parallel SCSI connectors, allowing for the small 2.5-inch (64 mm) drives. SAS currently supports point data transfer speeds up to 6 Gbit/s, but is expected to reach 12 GBit/s in near future SFF

8482,SATA

connector,

Internal

connector ,connected with 1 device, Formfactor compatible with SATA: allows for SATA drives to connect to a SAS backplane, which obviates the need to install an additional SATA controller just to attach a DVD-writer, for example. Note that SAS drives are not usable on a SATA bus and have their physical connector keyed to prevent any plugging into a SATA backplane. SFF 8484,Internal connector with 32 pins and can be connected to 4 devices, Hi-density internal connector, 2 and 4 lane versions are defined by the SFF standard.

SFF 8470,Infiniband connector is an External connector with 32 pins and can be connected to 4 devices, Hi-density external connector (also used as an internal connector) SFF 8088,External mini-SAS, External mSAS connector with 26 pins and [Type text]

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can be connected to 4 devices, Molex iPASS reduced width external 4× connector with future 10 Gbit/s support

External Device Interfaces External Devices can be interfaced using interfacing technologies like Parallel Port (LPT), Serial port USB and PS/2 connectors; the following describes them.

Parallel Port (LPT) A parallel port is a type of interface found on computers (personal and otherwise) for connecting various peripherals. It is also known as a printer port or Centronics port. The Parallel Port is the most commonly used port for interfacing home made projects. This port will allow the input of up to 9 bits or the output of 12 bits at any one given time, thus requiring minimal external circuitry to implement many simpler tasks. The port is composed of 4 control lines, 5 status lines and 8 data lines. It's found commonly on the back PC as a D-Type 25 Pin female connector. There may also be a D-Type 25 pin male connector. This will be a serial RS-232 port and thus, is a totally incompatible port. Parallel port works in 5 modes which are as follows, 1. Compatibility Mode. 2. Nibble Mode. (Protocol not Described in this Document) 3. Byte Mode. (Protocol not Described in this Document) 4. EPP Mode (Enhanced Parallel Port). 5. ECP Mode (Extended Capabilities Mode). The aim was to design new drivers and devices which were compatible with each other and also backwards compatible with the Standard Parallel Port (SPP). Compatibility, Nibble & Byte modes use just the standard hardware available on the original Parallel Port cards while EPP & ECP modes require additional hardware which can run at faster speeds, while still being downwards compatible with the Standard Parallel Port. Compatibility mode or "Centronics Mode" as it is commonly known, can only send data in the forward direction at a typical speed of 50 Kbytes/sec but can be as high as 150+ Kbytes/sec. In order to receive data, you must change the mode to either Nibble or Byte mode. Nibble mode can input a nibble (4 bits) in the reverse direction. E.g. from device to computer. Byte mode uses the Parallel's bi-directional feature (found only on some cards) to input a byte (8 bits) of data in the reverse direction. Extended and Enhanced Parallel Ports use additional hardware to generate and manage handshaking. To output a byte to a printer (or anything in that matter) using compatibility mode, the software must, [Type text]

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1. Write the byte to the Data Port. 2. Check to see is the printer is busy. If the printer is busy, it will not accept any data, thus any data which is written will be lost. 3. Take the Strobe (Pin 1) low. This tells the printer that there is the correct data on the data lines. (Pins 2-9) 4. Put the strobe high again after waiting approximately 5 microseconds after putting the strobe low. (Step 3) This limits the speed at which the port can run at. The EPP & ECP ports get around this by letting the hardware check to see if the printer is busy and generate a strobe and /or appropriate handshaking. This means only one I/O instruction need to be performed, thus increasing the speed. These ports can output at around 1-2 megabytes per second. The ECP port also has the advantage of using DMA channels and FIFO buffers, thus data can be shifted around without using I/O instructions. Hardware Properties Below is a table of the "Pin Outs" of the D-Type 25 Pin connector and the Centronics 34 Pin connector. The D-Type 25 pin connector is the most common connector found on the Parallel Port of the computer, while the Centronics Connector is commonly found on printers. The IEEE 1284 standard however specifies 3 different connectors for use with the Parallel Port. The first one, 1284 Type A is the D-Type 25 connector found on the back of most computers. The 2nd is the 1284 Type B which is the 36 pin Centronics Connector found on most printers. Pin No (D-Type 25) 1 2 3 4 5 6 7 8 9 10 11 12

Pin No (Centronic s) 1 2 3 4 5 6 7 8 9 10 11 12

13 14

13 14

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SPP Signal

Directio n In/out

Registe r

nStrobe Data 0 Data 1 Data 2 Data 3 Data 4 Data 5 Data 6 Data 7 nAck Busy Paper-Out / Paper-End Select nAuto-Linefeed

In/Out Out Out Out Out Out Out Out Out In In In

Control Data Data Data Data Data Data Data Data Status Status Status

In In/Out

Status Control Page 39

15 16 17

32 31 36

18 - 25

19-30

nError / nFault In nInitialize In/Out nSelect-Printer / In/Out nSelect-In Ground Gnd

Status Control Control

The output of the Parallel Port is normally TTL logic levels. The voltage levels are the easy part. The current you can sink and

source varies from port to port. Most Parallel Ports implemented in ASIC, can sink and source around 12mA. However these are just some of the figures taken from Data sheets, Sink/Source 6mA, Source 12mA/Sink 20mA, Sink 16mA/Source 4mA, Sink/Source 12mA.

Centronics Centronics is an early standard for transferring data from a host to the printer. The majority of printers use this handshake. This handshake is normally implemented using a Standard Parallel Port under software control. Below is a simplified diagram of the `Centronics' Protocol. Data is first applied on the Parallel Port pins 2 to 7. The host then checks to see if the printer is busy. i.e. the busy line should be low. The program then asserts the strobe, waits a minimum of 1uS, and then de-asserts the strobe. Data is normally read by the printer/peripheral on the rising edge of the strobe. The printer will indicate that it is busy processing data via the Busy line. Once the printer has accepted data, it will acknowledge the byte by a negative pulse about 5uS on the nAck line.Quite often the host will ignore the nAck line to save time. Latter in the Extended Capabilities Port, the hardware do all the handshaking for you. All the programmer must do is write the byte of data to the I/O port. The hardware will check to see if the printer is busy, generate the strobe. Note that this mode commonly doesn't check the nAck either. Port Addresses The Parallel Port has three commonly used base addresses. The 3BCh base address was originally introduced used for Parallel Ports on early Video Cards. This address then disappeared for a while, when Parallel Ports were later removed from Video Cards. They has now reappeared as an option for Parallel Ports integrated onto motherboards, upon which their configuration can be changed using BIOS. LPT1 is normally assigned base address 378h, while LPT2 is assigned 278h. 378h & [Type text]

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278h have always been commonly used for Parallel Ports. These addresses may change from machine to machine. Address

Notes:

3BCh - 3BFh

Used for Parallel Ports which were incorporated on to Video Cards - Doesn't support ECP addresses

378h - 37Fh

Usual Address For LPT 1

278h - 27Fh

Usual Address For LPT 2

When the computer is first turned on, BIOS (Basic Input/Output System) will determine the number of ports you have and assign device labels LPT1, LPT2 & LPT3 to them. BIOS first looks at address 3BCh. If a Parallel Port is found here, it is assigned as LPT1, then it searches at location 378h. If a Parallel card is found there, it is assigned the next free device label. This would be LPT1 if a card wasn't found at 3BCh or LPT2 if a card was found at 3BCh. The last port of call, is 278h and follows the same procedure than the other two ports. Therefore it is possible to have a LPT2 which is at 378h and not at the expected address 278h. What can make this even confusing, is that some manufacturers of Parallel Port Cards, have jumpers which allow you to set your Port to LPT1, LPT2, LPT3. Now what address is LPT1? - On the majority of cards LPT1 is 378h, and LPT2, 278h, but some will use 3BCh as LPT1, 378h as LPT1 and 278h as LPT2. The assigned devices LPT1, LPT2 & LPT3 should not be a worry to people wishing to interface devices to their PC's. Most of the time the base address is used to interface the port rather than LPT1 etc. However to find the address of LPT1 or any of the Line Printer Devices, we can use a lookup table provided by BIOS. Start Address

Function

0000:0408

LPT1's Base Address

0000:040A

LPT2's Base Address

0000:040C

LPT3's Base Address

0000:040E

LPT4's Base Address (Note 1)

Parallel Port Modes in BIOS Today, most Parallel Ports are multimode ports. They are normally software configurable to one of many modes from BIOS. The following modes are configurable via BIOS. The typical modes are,

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Printer Mode Standard & Bi-directional (SPP) Mode EPP1.7 and SPP Mode EPP1.9 and SPP Mode ECP Mode ECP and EPP1.7 Mode ECP and EPP1.9 Mode Printer Mode is the most basic mode. It is a Standard Parallel Port in forward mode only. It has no bi-directional feature, thus Bit 5 of the Control Port will not respond. Standard & Bi-directional (SPP) Mode is the bi-directional mode. Using this mode, bit 5 of the Control Port will reverse the direction of the port, so you can read back a value on the data lines. EPP1.7 and SPP Mode is a combination of EPP 1.7 (Enhanced Parallel Port) and SPP Modes. In this mode of operation you will have access to the SPP registers (Data, Status and Control) and access to the EPP Registers. In this mode you should be able to reverse the direction of the port using bit 5 of the control register. EPP 1.7 is the earlier version of EPP. EPP1.9 and SPP Mode is just like the previous mode, only it uses EPP Version 1.9 this time. As in the other mode, you will have access to the SPP registers, including Bit 5 of the control port. However this differs from EPP1.7 and SPP Mode as you should have access to the EPP Timeout bit. ECP Mode will give you an Extended Capabilities Port. The mode of this port can then be set using the ECP's Extended Control Register (ECR). However in this mode from BIOS the EPP Mode (100) will not be available. ECP and EPP1.7 Mode and ECP and EPP1.9 Mode will give you an Extended Capabilities Port, just like the previous mode. However the EPP Mode in the ECP's ECR will now be available.

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Pin configuration

LPT Male and Female cable

Serial Port Serial port is a serial communication physical interface through which information transfers in or out one bit at a time (contrast parallel port). While such interfaces as Ethernet, FireWire, and USB all send data as a serial stream, the term "serial port" usually identifies hardware more or less compliant to the RS-232 standard, intended to interface with a modem or with a similar communication device. For its use to connect peripheral devices, the serial port has largely been replaced by USB and Firewire. For networking, it has been replaced by Ethernet. Serial ports are commonly still used in legacy applications such as industrial automation systems, scientific analysis, shop till systems and some industrial and consumer products. Network equipment (such as routers and switches) often use serial console for configuration. Serial ports are still used in these areas as they are simple, cheap and their console functions (RS-232) are highly standardized and widespread. The vast majority of computer systems have a serial port, however it must usually be wired manually and sometimes there are no pins in the manufactured version.

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Hardware Some computers, such as the IBM PC, used an integrated circuit called a UART, that converted characters to (and from) asynchronous serial form, and automatically looked after the timing and framing of data. Very low-cost systems, such as some early home computers, would instead use the CPU to send the data through an output pin, using the so-called bit-banging technique. Many personal computer motherboards still have at least one serial port. Small-form-factor systems and laptops may omit RS-232 connector ports to conserve space, but the electronics are still there. RS232 has been standard for so long that the circuits needed to control a serial port became very cheap and often exist on a single chip, sometimes also with circuitry for a parallel port. Early home computers often had proprietary serial ports with pinouts and voltage levels incompatible with RS232. Inter-operation with RS-232 devices may be impossible as the serial port cannot withstand the voltage levels produced and may have other differences that "lock in" the user to products of a particular manufacturer. Low-cost processors now allow higher-speed, but more complex, serial communication standards such as USB and FireWire to replace RS-232. These make it possible to connect devices that would not have operated feasibly over slower serial connections, such as mass storage, sound, and video devices. Connectors While the RS-232 standard originally specified a 25-pin D-type connector, many designers of personal computers chose to implement only a subset of the full standard: they traded off compatibility with the standard against the use of less costly and more compact connectors (in particular the DE-9 version used by the original IBM PC-AT). Starting around the time of the introduction of the IBM PC-AT, serial ports were commonly built with a 9-pin connector to save cost and space. However, presence of a nine pin D-subminiature connector is neither necessary nor sufficient to indicate use of a serial port, since this connector was also used for video, joysticks, and other purposes. Some miniaturized electronics, particularly graphing calculators and to a lesser extent hand-held amateur and two-way radio equipment, have serial ports using a jack plug connector, usually the smaller 2.5 or 3.5 mm connectors and use the most basic 3-wire interface. Many models of Macintosh favored the related (but faster) RS-422 standard, mostly using German Mini-DIN connectors, except in the earliest models. The Macintosh included a standard set of two ports for connection to a printer and a modem, but some PowerBook laptops had only one combined port to save space. Pinouts [Type text]

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The following table lists commonly-used RS-232 signals and pin assignments Signal Name Common Ground Protective Ground Transmitted Data Received Data Data Terminal Ready Data Set Ready Request To Send Clear To Send Carrier Detect Ring Indicator

Origin DB-25 DE-9 (TIA-574) Abbreviation DTE DCE G 7 5 PG 1 TxD ● 2 3 RxD ● 3 2 DTR ● 20 4 DSR ● 6 6 RTS ● 4 7 CTS ● 5 8 DCD ● 8 1 RI ● 22 9

Signals Transmitted Data (TxD)

Data sent from DTE to DCE.

Received Data (RxD)

Data sent from DCE to DTE.

Request To Send (RTS)

Asserted (set to logic 0, positive voltage) by DTE to prepare DCE to

receive data. This may require action on the part of the DCE, e.g. transmitting a carrier or reversing the direction of a half-duplex channel. For the modern usage of "RTS/CTS handshaking," see the section of that name. Ready To Receive (RTR) Asserted by DTE to indicate to DCE that DTE is ready to receive data. If in use, this signal appears on the pin that would otherwise be used for Request To Send, and the DCE assumes that RTS is always asserted; see RTS/CTS handshaking for details. Clear To Send (CTS)

Asserted by DCE to acknowledge RTS and allow DTE to transmit. This

signaling was originally used with half-duplex modems and by slave terminals on multidrop lines: The DTE would raise RTS to indicate that it had data to send, and the modem would raise CTS to indicate that transmission was possible. For the modern usage of "RTS/CTS handshaking," see the section of that name. Data Terminal Ready (DTR) Asserted by DTE to indicate that it is ready to be connected. If the DCE is a modem, this may "wake up" the modem, bringing it out of a power saving mode. This behavior is seen quite often in modern PSTN and GSM modems. When this signal is de-asserted, the modem may return to its standby mode, immediately hanging up any calls in progress.

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Data Set Ready (DSR)

Asserted by DCE to indicate the DCE is powered on and is ready to

receive commands or data for transmission from the DTE. For example, if the DCE is a modem, DSR is asserted as soon as the modem is ready to receive dialing or other commands; DSR is not dependent on the connection to the remote DCE (see Data Carrier Detect for that function). If the DCE is not a modem (e.g. a null modem cable or other equipment), this signal should be permanently asserted (set to 0), possibly by a jumper to another signal. Data Carrier Detect (DCD) Asserted by DCE when a connection has been established with remote equipment. Ring Indicator (RI) Asserted by DCE when it detects a ring signal from the telephone line.

Universal Serial Bus A USB system has an asymmetric design, consisting of a host, a multitude of downstream USB ports, and multiple peripheral devices connected in a tiered-star topology. Additional USB hubs may be included in the tiers, allowing branching into a tree structure with up to five tier levels. A USB host may have multiple host controllers and each host controller may provide one or more USB ports. Up to 127 devices, including the hub devices, may be connected to a single host controller. USB devices are linked in series through hubs. There always exists one hub known as the root hub, which is built into the host controller. So-called sharing hubs, which allow multiple computers to access the same peripheral device(s), also exist and work by switching access between PCs, either automatically or manually. They are popular in small-office environments. In network terms, they converge rather than diverge branches. A physical USB device may consist of several logical sub-devices that are referred to as device functions. A single device may provide [Type text]

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several functions, for example, a webcam (video device function) with a built-in microphone (audio device function). Such a device is called a compound device in which each logical device is assigned a distinctive address by the host and all logical devices are connected to a built-in hub to which the physical USB wire is connected. A host assigns one and only one device address to a function. USB device communication is based on pipes (logical channels). Pipes are connections from the host controller to a logical entity on the device named an endpoint. The term endpoint is occasionally used to incorrectly refer to the pipe because, while an endpoint exists on the device permanently, a pipe is only formed when the host makes a connection to the endpoint. Therefore, when referring to the connection between a host and an endpoint, the term pipe should be used. A USB device can have up to 32 active pipes, 16 into the host controller and 16 out of the controller. There are two types of pipes: stream and message pipes. A stream pipe is a uni-directional pipe connected to a uni-directional endpoint that is used for bulk, interrupt, and isochronous data flow while a message pipe is a bi-directional pipe connected to a bi-directional endpoint that is exclusively used for control data flow. An endpoint is made into the USB device by the manufacturer, and therefore, exists permanently. An endpoint of a pipe is addressable with tuple (device_address, endpoint_number) as specified in a TOKEN packet that the host sends when it wants to start a data transfer session. If the direction of the data transfer is from the host to the endpoint, an OUT packet, which is a specialization of a TOKEN packet, having the desired device address and endpoint number is sent by the host. If the direction of the data transfer is from the device to the host, the host sends an IN packet instead. If the destination endpoint is a unidirectional endpoint whose manufacturer's designated direction does not match the TOKEN packet (e.g., the manufacturer's designated direction is IN while the TOKEN packet is an OUT packet), the TOKEN packet will be ignored. Otherwise, it will be accepted and the data transaction can start. A bi-directional endpoint, on the other hand, accepts both IN and OUT packets. Endpoints are grouped into interfaces and each interface is associated with a single device function. An exception to this is endpoint zero, which is used for device configuration and which is not associated with any interface. A single device function comprises of independently controlled interfaces is called a composite device. A composite device only has a single device address because the host only assigns a device address to a function. When a USB device is first connected to a USB host, the USB device enumeration process is started. The enumeration starts by sending a reset signal to the USB device. The speed of the USB device is determined during the reset signaling. After reset, the USB device's information is read by the host, then the device is assigned a unique 7-bit address. If the device is supported by the host, the device drivers needed for communicating with the device are loaded and the device is set to a configured state. If the USB host is restarted, the enumeration [Type text]

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process is repeated for all connected devices. The host controller directs traffic flow to devices, so no USB device can transfer any data on the bus without an explicit request from the host controller. In USB 2.0, the host controller polls the bus for traffic, usually in a round-robin fashion. The slowest device connected to a controller sets the speed of the interface. For SuperSpeed USB (USB 3.0), connected devices can request service from host, and because there are two separate controllers in each USB 3.0 host, USB 3.0 devices will transmit and receive at USB 3.0 speeds, regardless of USB 2.0 or earlier devices connected to that host. Operating speeds for them will be set in the legacy manner. PinOut

Pin 1 2 3 4

Signal VCC DD+ GND

Color Red White Green Black

Description +5V Data Data + Ground

Glossary Direct Attached Storage (DAS) refers to a digital storage system directly attached to a server or workstation, without a storage network in between. DAS system is made of a data storage device connected directly to a computer through a host bus adapter. Between those two points there is no network device (like hub, switch, or router), and this is the main characteristic of DAS. The main protocols used for DAS connections are ATA, SATA, SCSI, SAS, and Fibre Channel. A DAS device can be shared between multiple computers, if only it provides multiple interfaces (ports) that allow concurrent and direct access. This way it can be usable for computer clusters. DAS can enable storage capacity extension, while keeping high data bandwidth and access rate. Network Attached Storage (NAS) is essentially a self-contained computer connected to a network, with the sole purpose of supplying file-based data storage services to other devices on the [Type text]

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network. The unit is not designed to carry out general-purpose computing tasks, although it may technically be possible to run other software on it. NAS units usually do not have a keyboard or display, and are controlled and configured over the network, often by connecting a browser to their network address. The alternative to NAS storage on a network is to use a computer as a file server. In its most basic form a dedicated file server is no more than a NAS unit with keyboard and display and an operating system which, while optimised for providing storage services, can run other tasks. Despite differences SAN and NAS are not exclusive and may be combined in one solution: SANNAS hybrid. Storage Area Network (SAN) is a high-speed special-purpose network (or sub-network) that interconnects different kinds of data storage devices with associated data servers on behalf of a larger network of users. Typically, a storage area network is part of the overall network of computing resources for an enterprise. A storage area network is usually clustered in close proximity to other computing resources such as IBM z990 mainframes but may also extend to remote locations for backup and archival storage, using wide area network carrier technologies such as ATM or SONET. INCITS International Committee for Information Technology Standards, is an ANSI-accredited forum of IT developers. It was formerly known as the X3 and NCITS.INCITS technical standard groups and technical committees have provided many popular standards, among them are T10 SCSI, T11 (X3T9.3) - Fibre Channel and T13 - AT Attachment. INCITS coordinates technical standards activity between ANSI in the USA and joint ISO/IEC committees worldwide. This provides a mechanism to create standards that will be implemented in many nations. UDMA (with CRC) or Ultra Direct Memory Access was double transition clocking. Before Ultra DMA, one transfer of data occurred on each clock cycle, triggered by the rising edge of the interface clock (or "strobe"). With Ultra DMA, data is transferred on both the rising and falling edges of the clock. Ultra DMA also introduced the use of cyclical redundancy checking or CRC on the interface. The device sending data uses the CRC algorithm to calculate redundant information from each block of data sent over the interface. This "CRC code" is sent along with the data. On the other end of the interface, the recipient of the data does the same CRC calculation and compares its result to the code the sender delivered. If there is a mismatch, this means data was corrupted somehow and the block of data is resent. If errors occur frequently, the system may determine that there are hardware issues and thus drop down to a slower Ultra DMA mode, or even disable Ultra DMA operation. Memory Unit Conversion Table [Type text]

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Decimal

Symbol

Name

Binary Equivalent

103

K

Kilo

210=1024

106

M

Mega

220=1024 K

109

G

Giga

230=1024 M

1012

T

Tera

240=1024 G

1015

P

Peta

250=1024 T

1018

E

Exa

260=1024 P

1021

Z

Zetta

270=1024 E

1024

Y

Yotta

280=1024 Z

SCA Serial Connector Attachment, is a type of connection for the internal cabling of SCSI systems. There are two versions of this connector: the SCA-1, which is deprecated, and SCA-2, which is currently in use in most systems. In addition there are Single-Ended (SE) and Low Voltage Differential (LVD) types of the SCA. RAID Redundant Array of Inexpensive Disks is a technology that allowed computer users to achieve high levels of storage reliability from low-cost and less reliable PC-class disk-drive components, via the technique of arranging the devices into arrays for redundancy."RAID" is now used as an umbrella term for computer data storage schemes that can divide and replicate data among multiple hard disk drives. ST-506

was the first 5.25 inch hard disk drive. Introduced in 1980 by Seagate Technology, it

stored up to 5 MB. The similar 10 MB ST-412 was introduced in late 1981 with enhanced bit rates. ESDI

or Enhanced Small Disk Interface was a disc interface designed by Maxtor Corporation in

the early 1980s to be a follow-on to the ST-506 interface. ESDI used the same cabling as ST-506 and could handle data rates of 10, 15, or 20 MBits/sec (as opposed to ST-506's top speed of 7.5 megabits), and many high-end SCSI drives of the era were actually high-end ESDI drives with SCSI bridges integrated on the drive. Hot swapping and hot plugging are terms used to separately describe the functions of replacing system components without shutting down the system. Hot swapping describes changing components without significant interruption to the system, while hot plugging describes changing or adding components which interact with the operating system. Both terms describe the ability to remove and replace components of a machine, usually a computer, while it is operating. For hot swapping once the appropriate software is installed on the computer, a user can plug and unplug the [Type text]

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component without rebooting. A well-known example of this functionality is the Universal Serial Bus (USB) that allows users to add or remove peripheral components such as a mouse, keyboard, or printer. Native Command Queuing (NCQ) is a technology designed to increase performance of SATA hard disks under certain situations by allowing the individual hard disk to internally optimize the order in which received read and write commands are executed. This can reduce the amount of unnecessary drive head movement, resulting in increased performance for workloads where multiple simultaneous read/write requests are outstanding, most often occurring in server-type applications. Peripheral Component Interconnect(PCI) is a computer bus for attaching hardware devices in a computer. These devices can take either the form of an integrated circuit fitted onto the motherboard itself or a card fitted with motherboard. Typical PCI cards used in PCs include network cards, sound cards, modems, extra ports such as USB or serial, TV tuner cards and disk controllers. Open NAND Flash Interface (ONFI) are the small n very fast drives for storage. Low Insertion Force connectors are High-density metric (HDM) connectors from Molex are designed for board-to-board connection in applications such as networking, high-end computing and telecommunications equipment. HDM connectors offer a unique combination of robust mechanical performance, high speed and high-density signal capability. MultiDrop BUS is a computer bus in which all components are connected to the same set of electrical wires. A process of arbitration determines which device gets the right to be the sender of information at any point in time. The other devices must listen for the data that is intended to be received by them.but electronically are limited to around 200–400 MHz (because of reflections on the wire from the printed circuit board (PCB) onto the die) and 10–20 cm distance (SCSI-1 has 6 metres). Multidrop standards such as PCI are therefore being replaced by point-to-point. Backpane (or "backplane system") is a circuit board (usually a printed circuit board) that connects several connectors in parallel to each other, so that each pin of each connector is linked to the same relative pin of all the other connectors forming a computer bus. Different Voltage/Logic levels

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Terms VCC: The voltage applied to the power pin(s). In most cases the voltage the device needs to operate at. VIH: [Voltage Input High] The minimum positive voltage applied to the input which will be accepted by the device as a logic high. VIL: [Voltage Input Low] The maximum positive voltage applied to the input which will be accepted by the device as a logic low. VOL: [Voltage Output Low] The maximum positive voltage from an output which the device considers will be accepted as the maximum positive low level. VOH: [Voltage Output High] The maximum positive voltage from an output which the device considers will be accepted as the minimum positive high level. VT: [Threshold Voltage] The voltage applied to a device which is "transition-Operated", which cause the device to switch. May also be listed as a '+' or '-' value. RS232 logic level

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Different Data Transmission Protocols SPECIFICATIONS Mode of Operation Total Number of Drivers and Receivers on One Line (One driver active at a time for RS485 networks) Maximum Cable Length Maximum Data Rate (40ft. 4000ft. for RS422/RS485) Maximum Driver Output Voltage Driver Output Loaded Signal Level (Loaded Min.) Driver Output Unloaded Signal Level (Unloaded Max) Driver Load Impedance (Ohms) Max. Driver Current Power On in High Z State Max. Driver Current Power Off in High Z State Slew Rate (Max.) Receiver Input Voltage Range Receiver Input Sensitivity Receiver Input Resistance (Ohms), (1 Standard Load for RS485)

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RS232 SINGLE -ENDED 1 DRIVER 1 RECVR 50 FT. 20kb/s

RS423 SINGLE -ENDED 1 DRIVER 10 RECVR 4000 FT. 100kb/s

RS422 RS485 DIFFERENTIAL DIFFERENTIAL 1 DRIVER 10 RECVR

32 DRIVER 32 RECVR

4000 FT. 10Mb/s-100Kb/s

4000 FT. 10Mb/s-100Kb/s

+/-25V +/-5V to +/-15V

+/-6V +/-3.6V

-0.25V to +6V +/-2.0V

-7V to +12V +/-1.5V

+/-25V

+/-6V

+/-6V

+/-6V

3k to 7k N/A

>=450 N/A

100 N/A

54 +/-100uA

+/-6mA @ +/-2v 30V/uS +/-15V +/-3V 3k to 7k

+/-100uA

+/-100uA

+/-100uA

Adjustable +/-12V +/-200mV 4k min.

N/A -10V to +10V +/-200mV 4k min.

N/A -7V to +12V +/-200mV >=12k

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Attention!! This is to kindly request to all the readers of this report that if they find any faults in this report or if they append this report to make it better, they are heartily welcomed for feedbacks and they are requested to please inform me through my mail id and they may send me the new report on it as well. This way we all can help to propagate the knowledge in this world of science. Please help me in this process…

Shubham Pandey [email protected] [Type text]

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