Peripheral devicesStorage devices

Storage Devices

Also called secondary storagestore data & programs permanently for future

usecan be used as both input & output devices

Magnetic Disk Storage

Most widely used storage mediumconsists of a round piece of plastic or metal,

the surface on which is covered by a magnetic materials.

e.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.

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.

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 DisksFixed in the System UnitConsists of one or more rigid

platters coated with a magnetic material

the platters, read/write heads, and the access arms that move the heads across the disk surface are all enclosed in an airtight, sealed case

Access 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).

hard 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

To connect a hard disk to a microcomputer motherboard, you must have a hard disk interface.

This component includes circuitry that conforms to a standard recognized by both the hard disk and the motherboard manufacturer.

Common standards are Integrated Drive Electronics (IDE) and Small Computer System Interface (SCSI).

Removable DisksProvide both the storage capacity and fact a

ccess time of hard disk and the probability of floppy disks.

Examples: Iomega’s ZIP (100MB) JAZ (1-2 GB) Imation’s Superdisk (120MB)

Maintaining Stored Data

To prevent loss of data, 2 procedures should be performed regularly: Backup

process of creating a copy of important programs and data

Defragmentationprocess of reorganizing data stored on a disk so that file

s are located in contiguous (adjacent) clusters.

CD-ROM and Optical DisksBy using laser technology, optical disk can

store large quantities of dataa high power laser writes data on an optical

disk by burning microscopic holes on the disk surface

a lower power laser reads the data by reflecting light off the disk surface. The reflected light is converted into a series of bits

CD-ROM CD-Read Only Memory can store 650 MB data suitable for reference material such as encyclopedias, catalogs

and pictures

CD-R CD-Recordable write once, read many

CD-RW CD-Rewritable erasable; write many, read many

MO Magneto-Optical Floptical (Optical & Magnetic)

Magnetic TapeConsists of a thin ribbon of plastic, one side of which is

coated with a material that can be magnetized to record binary data.

A sequential storage media (must write and read records on after another)

usually cartridge tape serves as a primary means of

backup, a method of transferring data between system, and a cost-effective way to store data that does not have to be accessed

immediately

Other types of Storage Devices

PC Cards (PCMCIA)Flash Memory CardMemory StickSmart Card