About Io--182-2

GROUP 182 Adeline Halim Kesuma Bonifatio Hartono Maulahikmah Galinium Selvia Ettine Tania Puspita

General Overview † † †

Performance of I/O (B.51) CD (B.52) HardDisk (B.53)

Input/Output †

†

the collection of interfaces that different functional units (sub-systems) of an information processing system use to communicate with each other, or the signals (information) sent through those interfaces. I/O devices are used by a person (or other system) to communicate with a computer.

Performance †

I/O is major factor in system performance „

„ „ „

Demands CPU to execute device driver, kernel I/O code Context switches due to interrupts Data copying Network traffic especially stressful

Intercomputer Communication

*Operating systems concepts by Schilberschatz

Device Driver †

A device driver, or a software driver is a specific type of computer software, typically developed to allow interaction with hardware devices.

Daemon †

†

a daemon is a computer program that runs in the background Typically daemons have names that end with the letter "d"; for example, syslogd is the daemon which handles the system log.

Context Switch †

†

A context switch is the computing process of storing and restoring the state (context) of a CPU such that multiple processes can share a single CPU resource. The context switch is an essential feature of a multitasking operating system.

Intercomputer Communication

*Operating systems concepts by Schilberschatz

Model I/O I/O device consists of layer: Application Kernel Device-driver Device-controller Device

Compact Disc

* http://en.wikipedia.org/wiki/CD

Compact Disc †

†

A Compact Disc (CD) is an optical disc used to store digital data The CD, available on the market in late 1982, remains the standard physical medium for commercial audio recordings as of 2006.

Compact Disk Physical Details †

†

made from a 1.2 mm thick disc of very pure polycarbonate plastic. A thin layer of Super Purity Aluminium (or rarely gold, used for its data longevity, such as in some limited-edition audiophile CDs) is applied to the surface to make it reflective, which is protected by a film of lacquer.

Compact Disc shapes and diameters †

Standard CDs are available in two sizes: „

„

120 mm in diameter, with a 74 or 80minute audio capacity and a 650 or 700 MB data capacity 80 mm discs ("Mini CDs") were originally designed for CD singles and can hold up to 21 minutes of music or 184 MB of data.

CD Data Format †

†

†

a block of 8-bit data transformed into a 14-bit symbol using an errorcorrection method (Hamming code) A frame is made of 42 symbols(14 bits/symbol) A sector is made of 96 frames

CD Data format

*Foundation of computer science by forouzan.

CD Main physical parameters The main parameters of the CD are as follows: † Scanning velocity: 1.2–1.4 m/s (constant linear velocity) † Track pitch: 1.6 µm. † Disc diameter 120 mm. † Disc thickness: 1.2 mm. † Inner radius program area: 25 mm. † Outer radius program area: 58 mm. † Center spindle hole diameter: 15 mm

CD drives Speeds Speed

Data Rate (bps)

Approx (Kbps)

1x

153,600

150

2x

307,200

300

4x

614,400

600

6x

921,600

900

8x

1,228,800

1200

12x

1,843,200

1800

16x

2,457,600

2400

24x

3,688,400

3600

32x

4,915,200

4800

40x

6,144,000

6000

Types of CD’s † † † †

CD- Audio CD-ROM CD-R CD-RW

CD-Audio †

†

†

Standard CD format for storing audio soundtracks. Developed in 1980 by Sony and Phillips Based on the Red book Standard

CD-ROM † †

†

A Version of the CD Is a Compact Disc Read Only Memory that contains data accessible by a computer. Used to distribute computer software

CD-ROM Physical Details †

†

†

†

CD-ROM discs are identical in appearance to audio CDs Data is stored and retrieved in a very similar manner with CDs Can only be used with a computer equipped with a CD-ROM drive. Based on the yellow book standard

Creation and use of CDROM/CD-Audio

*Foundation of computer science by forouzan.

CD-ROM Reading †

Is read using a low-power laser beam coming from the computer drive.

CD-R †

†

†

Compact Disc-Recordable is a variation of the Compact Disc digital audio disc. CD-R is a write once, read-only medium CD-R cannot be erased and rerecorded.

CD-R Physical characteristics †

†

A standard CD-R is a 1.2 mm thick disc made of polycarbonate with a 120 mm or 80 mm diameter. Based on the orange book standard

Making a CD-R

*Foundation of computer science by forouzan.

CD-R Reading †

Can be read by a CD-ROM or a CD-R drive also using a low-power laser beam

CD-RW † †

†

†

Compact Disc Re-Writeable A type of CD disk that enables you to write onto it in multiple sessions. The first CD-RW drives became available in mid-1997. Based on the orange book standard

Making a CD-RW

*Foundation of computer science by forouzan.

CD-RW Reading †

Uses the same type of low-power laser beam as CD-R and CD-ROM

Hard Disk †

A hard disk drive is a digitally encoded non-volatile storage device which stores data on rapidly rotating platters with magnetic surfaces.

Hard Disk Drive Evolution

*www.storagereview.com

HDD Anatomy I The main parts of a hard disk are: • Platters • Spindle and Spindle Motor • Read/Write Heads • Head Actuator

HDD Anatomy II

*www.storagereview.com

HDD Anatomy: Platters †

†

†

The platters are the actual disks inside the drive that store the magnetized data. They are composed of two substances: „ A substrate material that forms the bulk of the platter and gives it structure and rigidity „ A magnetic media coating which actually holds the magnetic impulses that represent the data Each platter is magnetized on each side.

HDD Anatomy: Platters (Tracks and Sectors) †

†

Tracks are concentric circles placed on the surface of each platter on which all information stored on a hard disk is recorded. Each track is broken into smaller units called sectors.

*www.storagereview.com

HDD Anatomy: Platters (Cylinders) †

A cylinder is the set of all tracks that all the heads are currently located at.

*www.storagereview.com

HDD Anatomy: Spindle and Spindle Motor †

†

†

†

The platters are clamped to a spindle that rotates all the platters in unison. The spindle motor is built right into the spindle or mounted directly below it. The motor spins at a constant set rate ranging from 3,600 to 10,000 RPM. The motor is attached to a feedback loop to ensure that it spins at precisely the speed it is supposed to.

HDD Anatomy: Read/Write Heads †

†

† †

The read/write heads are the interface between the magnetic physical media on which the data is stored and other electronic components of the hard disk (and the PC). The heads convert bits to magnetic pulses and store them on the platters, and then reversing the process when the data needs to be read back. Only one head can be active at one time. There is one head per platter side.

HDD Anatomy: Head Actuator Assembly †

†

The heads are mounted on head sliders, which are suspended over the surface of the disk at the ends of the head arms. The head arms are all mechanically fused into a single structure that is moved around the surface of the disk by the actuator. *www.storagereview.com

Data Access †

†

Data is accessed by moving the heads from the inner to the outer part of the disk, driven by the head actuator. There are several interface standards for passing data between a hard disk and a computer. The most common are IDE and SCSI.

Hard Disk Performance Specification: Seek Time †

†

The seek time of a hard disk measures the amount of time required for the read/write heads to move between tracks over the surfaces of the platters. 3 types of seek time specification: average, track to track, full stroke.

Hard Disk Performance Specification: Settle Time †

The settle time specification (sometimes called settling time) refers to the amount of time required, after the actuator has moved the head assembly during a seek, for the heads to stabilize sufficiently for the data to begin to be read.

Hard Disk Performance Specification: Command Overhead Time †

Command overhead refers to the time that elapses from when a command is given to the hard disk until something actually starts happening to fulfill the command.

Hard Disk Performance Specification: Latency †

†

Latency is defined as the time it takes to position the proper sector under the read/write head. The faster the disk is spinning, the quicker the correct sector will rotate under the heads, and the lower latency will be.

Hard Disk Performance Specification: Access Time †

†

Access time in general is the time a hard disk takes to locate a single piece of information and make it available for processing. Access Time = Command Overhead Time + Seek Time + Settle Time + Latency

Questions & Answers from “Monkey Book”

Overview †

INPUT/OUTPUT (B.51) - Improve efficiency of I/O - Model I/O

†

CD (B.52) - Differences among CD’s - CD-ROM Speed

†

HardDisk I (B.53) - Time Latency

B.51. INPUT/OUTPUT a. Briefly explain at least 6 principles to improve the efficiency of I/O!

Several principles to improve the efficiency of I/O: † †

†

Reduce the number of context switches Reduce the number of times that must be copied in memory while passing between device and application Reduce the frequency of interrupts by using large transfers, smart controllers and polling (if busy waiting can be minimized)

B.51. INPUT/OUTPUT(Cont’d) †

†

†

Increase concurrency by using DMAknowledgeable controllers or channels to offload simple data copying from the CPU Move processing primitives into hardware, to allow their operation in device controllers concurrent with the CPU and bus operation. Balance CPU, memory subsystem, bus, and I/O performance, because an overload in any one area will cause idleness in others.

B.51. INPUT/OUTPUT(Cont’d) b. It is known that an I/O device consists of layers, which are: Application, Kernel, device-driver, device-controller, and device. Please explain how choosing these layers effect the development of a new application. Discuss these aspects: The development time, efficiency, development cost, abstraction, and flexibility.

B.51. INPUT/OUTPUT(Cont’d)

*Operating systems concepts by Schilberschatz

B.51. INPUT/OUTPUT(Cont’d) †

I/O algorithm is implemented at application level because application code is the most flexible. Furthermore, by developing code at the application level, we avoid the need to reboot or reload device-drivers after every change to the code. Application level implementation can be inefficient, because of the overhead of context switches and because the application cannot take advantage of internal kernel data structures and kernel functionality. The most efficient is the hardware. Besides that, the hardware also increase development time, development cost and abstraction.

B.51. INPUT/OUTPUT(Cont’d) †

The highest performance may be obtained by a specialized implementation in hardware, either in device or in the controller. The disadvantages of a hardware implementation include the difficulty and expense of making further improvements or of fixing bugs, the increased development time and the decreased flexibility.

B.52. CD-ROM a. Please explain the differences between CD-Audio, CD-ROM, CD-R, and CD-RW! CD-Audio

CD-ROM

CD-R

CD-RW

Year

1982

1984

Mid 1990’s

Mid 1997

Diameter

120mm/80mm

120mm/80mm

120mm/80mm

120mm/80mm

Thick

1.2 mm

1.2 mm

1.2 mm

1.2 mm

Data type

Audio only

Data-audio

Data-audio

Data-audio

capability

Write once by manufacture

Write once by manufacture

WORM

Re-writeable

The creation

Using a master disc

Using a master disc

No master disc

No Master Disc

Reading

Low laser beam

Low laser beam

Low laser beam

Low laser beam

Material to simulate pits

Polycarbonate resin

Polycarbonate resin

dye

alloy of silver indium, antimony, and tellurium

Specification

Red-book

Yellow-book

Orange-book

Orange-book

B.52. CD-ROM (Cont’d) b. The early CD-Audio (650 MB) has 74 minutes duration. Calculate the transfer speed of a CD-ROM Reader with the speed of “37 x”. †

†

The CD-ROM Reader duration: 74 minutes / 37 = 2 minutes The CD-ROM Reader transfer speed: 650 MB / 120 seconds = 5.417 MB/second

B.53. Hard Disk 1 † †

† †

†

A Disk with these specifications is known: 100 Gbytes capacity (assumption 1Gbytes = 1000 Mbytes) There are 2 plates, with 2 surfaces each Amount of tracks = 2500 (revolution: 6000 RPM) At one time, there is one HEAD (on one side) that is active

B.53. Hard Disk 1(Cont’d) a. How much is the maximum rotational latency delay of the DISK? † 6000 RPM = 100 RPS † 1 revolution = 10 ms † So, the maximum time latency of the DISK is 10 ms.

B.53. Hard Disk 1(Cont’d) b.How much is the average time latency of the DISK? † The average time latency of the DISK = (10 ms + 0 ms) / 2 = 5 ms

B.53. Hard Disk 1(Cont’d) c. What is the minimum time (without latency and seek) needed to transfer 1 million (1000000) bytes data? † † † † †

There are two plates with two surfaces each, so the capacity of one surface is 25 Gbytes. One track has the capacity of: 25 Gbytes / 2500 = 10 Mbytes. The time needed to complete one revolution is 10 ms. So, the minimum time needed to transfer one million byte data is: (1 Mbytes / 10 Mbytes) × 10 ms = 1 ms

References † †

http://www.storagereview.com/guide/guide_index.html All pictures in the hard disk section are courtesy of www.storagereview.com

†

http://en.wikipedia.org/wiki/CD

†

Foundation of computer science by forouzan.

†

Operating systems concepts by Schilberschatz.

†

Copyright © 2006 Group 182. Verbatim Copying and Distribution of this entire article are permitted worldwide, without royalty, in any medium, provided this notice, and the copyright notice are preserved.