Information TechnologyInformation TechnologyStorage DevicesStorage Devices

Prof. Adnan KhalidProf. Adnan Khalid

Storage DevicesStorage Devices

In many cases the information that has been processed is stored in machine-readable format so that it may be accessed at a later time by a computer. This data is stored in binary form in 'bits'. This practice requires the use of storage devices. Storage Devices:

Hard Disk Magnetic Tape Floppy Disk Optical Disk Punched Cards USB Flash Drive Zip Disk Multimedia Cards

Hard DiskHard Disk

The hard disk is a direct-access storage medium with a rigid magnetic disk. The data is stored as magnetized spots arranged in concentric circles (tracks) on the disk. Each track is divided into sectors. The number of tracks and sectors on a disk is known as its 'format'.

Hard DiskHard Disk

High data rates demand that the disk rotates at a high speed (about 3,600 rpm). As the disk rotates read/write heads move to the correct track. The disk is sealed and lubricated and the head hovers on a cushion of air just above the disk to avoid damage. These are therefore called floating heads.

The storage capacity of a hard disk can be Gigabytes (Gb), i.e. thousands of Megabytes (1000Mb), of information.

Magnetic TapeMagnetic Tape

A recording medium consisting of a thin tape with a coating of a fine magnetic material, used for recording analogue or digital data. Data is stored in frames across the width of the tape. The frames are grouped into blocks or records which are separated from other blocks by gaps.

Magnetic tape is a serial access medium, similar to an audio cassette, and so data (like the songs on a music tape) cannot be quickly located.

However large amounts of information can be stored within magnetic tape. This characteristic has prompted its use in the regular backing up of hard disks.

Floppy DiskFloppy Disk

A floppy disk is a thin magnetic-coated disk contained in a flexible or semi-rigid protective jacket. Data is stored in tracks and sectors.

Floppy DiskFloppy Disk

The floppy disks are usually 3.5" in size. However, older floppy disks may be in use; these would be 5.25" in size.

Double sided high density 3.5" disks can hold 1.44 Mb of data.

Once data is stored on a floppy disk it can be 'write protected' by clicking a tab on the disk. This prevents any new data being stored or any old data being erased.

Optical DiskOptical Disk

An optical disk is impressed with a series of spiral pits in a flat surface.

A master disk is burnt by high-intensity laser beams in bit-patterns from which subsequent copies are formed which can be read optically by laser.

Examples CD and DVD

CDCD

The optical disk is a random access storage medium; information can be easily read from any point on the disk. A standard CD-ROM can store up to 650Mb of data, with 14,500 tracks per inch (tpi).

CD-ROM stands for Compact Disk - Read Only Memory. It is now possible to have CD-ROMs where extra tracks of information can be written onto them by the user. These are called read/writable CD-ROMs and these are becoming a popular and cheap method for storage.

DVDDVD

The DVD’s are also available in different formats that are the DVD +R, DVD-R, DVD RAM, DVD RW etc. The DVD has superb clarity when it is burnt as Digital Video Disk. The video that is stored over the disk is in the format that is supported by the DVD player. The DVD player that is available for the television sets is quite different from the one that is available for the computer systems.

Punched CardsPunched Cards

These are media which were popular in the past but their use required large storage space and was time-consuming. With the development of hard disks and other storage devices their use has practically disappeared.

USB Flash DriveUSB Flash Drive

A USB flash drive is much popular because of the size and the compactness. It actually behaves as if it is the portable hard drive. It has many provisions that provide you the option of transferring the data that is most important. The data transfer is an important part of any computer system. Also this type of the storage media can be used also for the back up or archiving of the small but important data like the personal or the business emails etc. The ease is that it can be carried in a pocket along with a keychain or so.

Zip DiskZip Disk

A Zip Drive is a 3.5" removable disk drive manufactured by Iomega. Zip disks come in various memory capacity models such as 100MB, 250MB and 750MB.

Zip disks were introduced in 1995 and were popularly used. The Zip drive is a medium-capacity removable disk storage system, introduced by Iomega in the year 1994. The Design concept of zip disk is based on Iomega's system; in which both systems have a set of read/write heads mounted over a rapidly spinning floppy disk. The Zip disk uses smaller media generally called as microfloppy, rather than the compact disc.

Multimedia CardMultimedia Card

The Multimedia Card is also known as flash memory card was developed in 1997 by Siemens. It has a flash memory which helps in portability of the Card when compared to Compact Flash.

The Multimedia card can provide storage for cell phones, PDAs and other devices. During 1997, the Multimedia card had a 4MB capacity and the weight of the card was not more than two grams. In 2005, Multimedia card can store up to 2GB.