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Storage Devices

Hard Drives
Floppy and Portable Drives

CD-ROM Drives

The CD-ROM(Compact Disc Read-Only Memory) are a computer adaption of the compact disc's used for audio systems. The standard CD-ROM can hold about 660 MB of computer information data.

The CD are coated with a layer of aluminiam and imprinted with a pattern of 'pits and flat' areas to denote the '1 and 0's that make up digital information data. To 'read' the disk a thin laser beam is focused onto the sections of the spinning disk. Light is reflected from the flat surfaces, but not from the pits, producing a on/off light effect. This sequence is then picked up by a photodetector and sent to the microprocessor as a series of 1's and 0's, which are then decoded.

The cost  CD-ROM's is now quite cheap with a 30X(30 times the speed of first series of CD-ROM's) now sells for about £40 and 24X for £30. Tranfer rates and normally between 1800-3600 KBytes/sec and access speeds of 75ms.

CD-ROM disk are read only media, the data being read from the innermost to the outermost edge.

The CD-Recordable drives (also called CD-R or WORM drives Write Once, Read Many times) can be used for archiving and permanent storage. The disks can only be used once to put data, or audio, onto. The CD-R disk has fallen in price to about £1 with and CD-Rwrit disks about £15. The newer read/write drive has now falled to about £250 - £500.

You add a CD-ROM drive to your system in much the same way as you add a floppy or hard disk. You can connect the modern drive to either an IDE socket on the mother board or SCSI adapter for a SCSI drive.

DVD-ROM drive

The DVD disk has a capacity of 17GB of data and are ideal for video films. It accomplishes this by having two reflecting layer's on each side of the disk (four layer in total). Information is first placed on the inner layer and then the beam is refocused to place information onto the outer layer. At present the drives can be purchased for about £200, inclusive of  an MPEG 2 video card. The drives are also backward compatible in that normal CD audio and CD-ROM disks can be played on them.

Hard Drives
Floppy and Portable Drives