Erasable Optical DiskA 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: 8
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