CD-ROM

Makes use of the accuracy of a low powered Laser beam and uses lenses, prisms and mirrors to read data
(as compared with magnetism for Standard Hard Disks).
Typical capacity(1998): 640MB
Compact disk (CD) technology
- CD-ROM ( Compact Disk Read Only Memory).
- CD-R: (Compact Disk recordable)
- CD-RW: (Compact Disk rewritable)
- PhotoCD
- WORM (Write Once Read Many)
Magneto-optical (MO) technology

Use

Can hold vast amounts of readily searched text
Useful for computer software distribution
- Windows 95, 98
- Visual Basic, Delphi
Can be creative, entertaining and educational
- Entertainment (Living books, Need for Speed, Myst),
- Education (Microsoft Encarta, Musical instruments)
- Information (Microsoft Encarta (Encyclopedia), MS Technical reference).

For writable CD-ROMS (CD-Recordable)

Share Electronic Files
- Sales tools, catalogs
- Home multimedia scrapbook
- Multimedia resume
Transport Large Files
- Multimedia presentations
- Pre-release software code
- Graphic files
Archive Data Permanently
- Taxes
- Blueprints
- Legal documents

hwsscdp1.gif (15989 bytes)

Instead of magnetising iron oxide particles a high power laser beam burns away a small pit for writing and a low power laser beam is reflected off the disk for reading.
Can be shared across a network

24x CD-ROM (Nov 1997)
Access Time [85-130msec]
Buffer size [128-512K]
Transfer rate MB/sec [approx. 3.6]
Burst Rate MB/sec [mostly 16.7]
RPM [approx 6K]
Mean time between failures(MTBF) in Power on hours (POH) [60K -125K]
(Nov 97) Proh Personal Computers

[CD-Rom]

CD-ROM ( Compact Disk Read Only Memory).
Data imprinted by the manufacturer, 540 to 738MB storage
PhotoCD
Developed by Kodak for storing digitised photos.
CD-R: (Compact Disk recordable)
- A plastic disk with a metal film, may be written to once by the user. Up to 650 MB
- Can have many format (see table below).
  Multi-session allows the CD to written to many times.
  (Most CD-ROM drives in PC's are still single session).
- or WORM (Write Once Read Many)
  An early form of optical technology. A metal film disk, may be written to once by the user. 122 to 640Mb storage. Still used by banks to make a permenant backup of data.
CD-RW : (Compact Disk rewritable)
- Data may be written and erased.
- (1998) Speed 2x write 6x read. Unfortunately not compatible with most CD-ROM drives in use today
  (Cost: HP CD-Writer Plus 7200i approx NZ$900)
  (Saarinen,J. & Sengstack, J., 1998 Jul)
- (1997) Early CD-RW drive in the NEXT computer. Stores 281 to 3200MB data

hwcd_3.gif (23848 bytes)