Storage Devices

STORAGE DEVICES

• There are many kinds of drives but when someone talks about a drive they usually mean a hard disk drive. • Most computers these days also come with a CD-ROM drive (that can be a player only or a player/recorder) or a DVD -ROM drive (again, either just a player or both a player and recorder). • Many computers also have a floppy disk drive.

• All the above disks are nonvolatile storage. • In other words whatever you store on the disk remains there, even after you shut off the PC. • Disk drives are encased in metal boxes to keep them from being damaged. • Hard disks are fixed disks whereas you can remove one disk and insert another in floppy drives and CD drives. • Hard drives and CD drives uses

• All the above drives need a data connector and a power connector. • A disk drive rotates the disk very fast and has one or more heads that read and write data. • There are different types of disk drives for different types of disks. • For example, a hard disk drive (HDD) reads and writes hard disks, and a floppy drive (FDD) accesses floppy disks. • A magnetic disk drive reads magnetic disks, and an optical drive reads optical disks.

Hard Disk • A hard disk drive (HDD), commonly referred to as a hard drive, hard disk or fixed disk drive, is a nonvolatile storage device which stores digitally encoded data on rapidly rotating platters with magnetic surfaces. • "drive" refers to a device distinct from its medium, such as a tape drive and its tape, or a floppy disk drive and its floppy disk. • Early HDDs had removable media; however, an HDD today is typically

Hard Disk Platters and actuator arms

record data by • HDDs magnetizing ferromagnetic material directionally, to represent either a 0 or a 1 binary digit. • They read the data back by detecting the magnetization of the material. • A typical HDD design consists of a spindle which holds one or more flat circular disks called platters, onto which the data is recorded.

• • The platters are spun at very high speeds. • Information is written to a platter as it rotates past devices called read-andwrite heads that operate very close (tens of nanometers in new drives) over the magnetic surface. • The read-and-write head is used to detect and modify the magnetization of the material immediately under it. • There is one head for each magnetic platter surface on the spindle, mounted on a common arm. • An actuator arm (or access arm) moves

Various components of a Hard Disk

IDE Cable A ty p ica l d e sk to p H D D , m ig h t sto re b e tw e e n 120 and 300 G B of d a ta , ro ta te a t 7 ,2 0 0 re v o lu tio n s per m in u te ( RPM ) and h a v e a m e d ia tra n sfe r ra te

• Hard disk drives are accessed over one of a number of bus types, including parallel ATA (PATA, also called IDE or EIDE), Serial ATA (SATA), SCSI, Serial Attached SCSI (SAS). • Following is the main difference between various connectors – IDE/ATA • • • • •

40-conductor connection (ATA) 80-conductor connection (UDMA) Max cable length 80” (0.46 mtrs) Max data transfer rate – 133Mbps Data transfer methods – PIO, DMA & ATAPI

–SATA • Serial connection • Max data transfer rate – 3 to 150 Mbps • Modular type connection 

–SCSI • 50-conductor connection • Max devices supported – up to 16 • Max data transfer rates – 5 to 160 Mbps

CD-ROM • CD-ROM (an abbreviation of "Compact Disc read-only memory") is a Compact Disc that contains data accessible by a computer. • While the Compact Disc format was originally designed for music storage and playback, the format was later adapted to hold any form of binary data. • CD-ROMs are popularly used to distribute computer software, including games and multimedia

CD-ROM • Some CDs hold both computer data and audio with the latter capable of being played on a CD player, whilst data (such as software or digital video) is only usable on a computer (such as PC CD-ROMs). • A CD has a single spiral track of data, circling from the inside of the disc to the outside.

CD • Discs are made from a 1.2 mm thick disc of polycarbonate plastic, with a thin layer of aluminum to make a reflective surface. 

• The most common size of CDROM disc is 120 mm in diameter, though the smaller Mini CD standard with an

Spiral tracks in a CD

• Data is stored on the disc as a series of microscopic indentations ("pits", with the gaps between them referred to as "lands"). • A laser is shone onto the reflective surface of the disc to read the pattern of pits and lands. • Because the depth of the pits is approximately one-quarter to onesixth of the wavelength of the laser light used to read the disc, the reflected beam's phase is shifted in relation to the incoming beam, causing destructive interference

DVD • Digital Versatile Disk has same size as a CD but stores seven times CD capacity on a single side. • DVDs can also be double-sided or dual layer. • Today most DVDs are used to display fulllength commercial motion pictures, plus additional material such as outtakes, director's notes, movie trailers, etc. • DVD, introduced in 1996, was originally known as Digital Video Disc but soon became known as Digital Versatile Disc. • It is the next generation of optical disc storage technology, which shares the same overall dimensions of a CD, but have significantly higher capacities - holding from 4 to 28 times as much data. • Single sided DVDs can store 4.7GB for

Blu-ray Disc • Blu-ray Disc (also known as Blu-ray or BD) is an optical disc storage medium. • Its main uses are high-definition video and data storage. • The disc has the same physical dimensions as standard DVDs and CDs. • The name Blu-ray Disc is derived from the blue laser (violet-colored) used to read and write this type of disc. • Because of the beam's shorter wavelength (405 nano meters), substantially more data can be stored on a Blu-ray Disc than on the DVD format, which uses a red (650 nm) laser. • A two-layer Blu-ray Disc can store 50

• During the format war over highdefinition optical discs, Blu-ray Disc competed with the HD DVD format. • On February 19, 2008, Toshiba—the main company supporting HD DVD— announced that it would no longer develop, manufacture, and market HD DVD players and recorders, leading almost all other HD DVD companies to follow suit, effectively ending the format war. • Blu-ray Disc was developed by the Bluray Disc Association, a group representing makers of consumer electronics, computer hardware, and motion pictures. • As of October 29, 2008, more than 1010 Blu-ray Disc titles have been

Flash Memory • Flash memory is an evolving technology. • The first generation of chips required that your PC or other device using the chips handle all the minute of the erase and write operations. • Current generation chips have their own onboard logic to automate these operations, making Flash ROM act more like ordinary memory. • The logic controls the timing of all the pulses used to erase and write to the chip, ensures that the proper voltages reach the memory cells, and even verifies that each write operation was carried out successfully. Fig. shows a type of Flash memory card. • On the other hand, the convenience of using Flash ROM has led many developers to create disk emulators from it. • For the most effective operation and longest

USB Flash drives F o r sy ste m d e sig n e rs , th e e le ctrica l re p ro g ra m m a b ility of F la sh R O M m a k e s it e a sy to u se . U n fo rtu n a te ly , F la sh R O M is h a n d ica p p e d b y th e sa m e lim ita tio n a s E E P R O M —its life is fin ite ( a lth o u g h lo n g e r th a n o rd in a ry E E P R O M ) a n d it m u st b e e ra se d a n d re p ro g ra m m e d a s one o r m o re b lo ck s in ste a d o f in d iv id u a l

• USB flash drives are typically removable and rewritable, much shorter than a floppy disk (1 to 4 inches or 2.5 to 10 cm), and weigh less than 2 ounces (56 g). • Storage capacities typically range from 64 MB to 64 GB with steady improvements in size and price per gigabyte. • Some allow 1 million write or

• A flash drive consists of a small printed circuit board protected inside a plastic, metal, or rubberized case, robust enough for carrying with no additional protection — in a pocket or on a key chain, for example. The USB connector is protected by a removable cap or by retracting into the body of the drive, although it is not liable to be