Peripheral devices Storage devices

Storage Devices zAlso called secondary storage zstore data & programs permanently for future use zcan be used as both input & output devices

Magnetic Disk Storage zMost widely used storage medium zconsists of a round piece of plastic or metal, the surface on which is covered by a magnetic materials. ze.g. floppy disks, hard disks and removable disk cartridge

Floppy Disk

Data is recorded on disk in concentric circular bands called tracks. The tracks on a disk are similar to the grooves on a phonograph record. Each track is divided into pie-shaped wedges called sectors. Two or more sectors combine to form a cluster.

Most computers maintain on the disk a table with the sector and track locations of data. This table, the file allocation table (FAT), enables the computer to locate data easily.

Hard Disks zFixed in the System Unit zConsists of one or more rigid platters coated with a magnetic material zthe platters, read/write heads, and the access arms that move the heads across the disk surface are all enclosed in an airtight, sealed case

zAccess time for a hard disk is significantly less than that for a floppy disk because a hard disk spins faster and unlike a floppy disk, a hard disk is spinning constantly (7200 revolutions per minute). zhard disks are permanently encased within the disk drive in a sealed environment free from dust and dirt. The disk can spin very rapidly, with the read/write head "floating" above the disk's surface.

Hard Disk Interfaces zTo connect a hard disk to a microcomputer motherboard, you must have a hard disk interface. zThis component includes circuitry that conforms to a standard recognized by both the hard disk and the motherboard manufacturer. zCommon standards are Integrated Drive Electronics (IDE) and Small Computer System Interface (SCSI).

Removable Disks zProvide both the storage capacity and fact access time of hard disk and the probability of floppy disks. zExamples: yIomega’s ZIP (100MB) yJAZ (1-2 GB) yImation’s Superdisk (120MB)

Maintaining Stored Data zTo prevent loss of data, 2 procedures should be performed regularly: yBackup xprocess of creating a copy of important programs and data yDefragmentation xprocess of reorganizing data stored on a disk so that files are located in contiguous (adjacent) clusters.

CD-ROM and Optical Disks zBy using laser technology, optical disk can store large quantities of data za high power laser writes data on an optical disk by burning microscopic holes on the disk surface za lower power laser reads the data by reflecting light off the disk surface. The reflected light is converted into a series of bits

zCD-ROM yCD-Read Only Memory ycan store 650 MB data ysuitable for reference material such as encyclopedias, catalogs and pictures zCD-R yCD-Recordable ywrite once, read many zCD-RW yCD-Rewritable yerasable; write many, read many zMO yMagneto-Optical yFloptical (Optical & Magnetic)

Magnetic Tape zConsists of a thin ribbon of plastic, one side of which is coated with a material that can be magnetized to record binary data. zA sequential storage media (must write and read records on after another) zusually cartridge tape zserves as a primary means of ybackup, ya method of transferring data between system, and ya cost-effective way to store data that does not have to be accessed immediately

Other types of Storage Devices zPC Cards (PCMCIA) zFlash Memory Card zMemory Stick zSmart Card