Erasable Optical Disk

A disk that uses optical technology but that can be easily erased and rewritten. A typical capacity is 650 Mbytes.

Both the audio and the CD-ROM share similar technology. The main difference is in the formats of data presentation.

Optical Storage CD-ROM

à Originally for audio

à 650 (775)Mbytes giving over 70(73.2) minutes audio

à Poly-carbonate coated with highly reflective coat (aluminum)

à Data stored as pits

à Reads by reflecting laser

à Constant packing density

à Constant linear velocity (1.2 m/s)

CD-ROM block Format

12 bytes 4 bytes 2046 bytes 288 bytes

Sync Id

2352 bytes

z Mode 0 = blank data field

z Mode 1 = 2048 bytes data+ error correction

z Mode 2 = 2336 bytes data

CD-ROM block Format consists of the following fields:

1. Sync: identifies the beginning of a block;

2. Header: contains the block address and the mode byte;

3. Data: User?s data;

4. Auxiliary: additional user?s data in mode 2. In mode 1, this is 288-bytes error-correcting code.

Random Access on CD-ROM

à Difficult

à Move head to rough position

à Set correct speed

à Read address

à Adjust to required location

Other Optical Storage

q CD-Writable

? WORM

? Now affordable

? Compatible with CD?ROM drives

q CD-RW

? Erasable

? Getting cheaper

? Mostly CD-ROM drive compatible

DVD Storage

q Digital Video Disk

? Used to indicate a player for movies

? Only plays video disks

q Digital Versatile Disk

? Used to indicate a computer drive

? Will read computer disks and play video disks

DVD technology

à Multi-layer

à Very high capacity (4.7 G per layer)

à Full length movie on single disk

? Using MPEG compression

à Finally standardised (honest!)

à Movies carry regional coding

à Players only play correct region films

à Can be ?fixed?

DVD-Writable

à Loads of trouble with standards

à First generation DVD drives may not read first generation DVD?W disks

à First generation DVD drives may not read CD-RW disks

Magnetic Tape

q Serial access

q Slow

q Very cheap

q Backup and archive

Date: 2016-06-13; view: 55