Docstoc

Compact disk

Document Sample
Compact disk Powered By Docstoc
					 Compact Disc - Manufacture Of A Compact Disc,
 Retrieving Information From A Disc, Drive
 Specifications, Care Of Cd-roms - CD-ROM drives,
 Drive formats, Interfaces, Nonstandard SCSI
 interfaces
In 1978, Philips and Sony together launched an effort to produce an audio
compact disc (CD) as a method of delivering digital sound and music to
consumers. The two companies continued to cooperate through the 1980s and
eventually worked out standards for using the CD technology to store computer
data. These recommendations evolved into the CD-ROM technology of today.


The CD-ROM (compact disc-read only memory) is a read-only optical storage
medium capable of holding 600 megabytes of data (approximately 500,000
pages of text), 70 minutes of high fidelity audio, or some combination of the two.
Legend has it that the size of the compact disc was chosen so that it could
contain a slow-tempo rendition of Beethoven's Ninth Symphony. As can be seen
from Table 1, compact discs offer a high volume of data storage at a lower cost
than other media.


The first users of CD-ROMs were owners of large databases: library catalogs,
reference systems, and parts lists. Typical applications of CD-ROMs as storage
media now include storage of such information as the following:


       every listing from all of the Yellow Pages in the United States
       maps of every street in the country
       facsimile numbers for all publicly held businesses and government institutions
       a 21-volume encyclopedia

The extremely thin metal layer of the CD, usually pure aluminum, reflects light from a tiny

infrared laser as the disc spins in the CD player. The reflections are transformed into electrical

signals and then further converted into meaningful data for use in digital equipment. © Kelly A.

Quin. Reproduced by permission.
CD-ROMs are expected to achieve significant impact in storage of the following
kinds of documents:


      business reference materials
      interactive educational materials for schools
      scholarly publications
      government archives
      home-based reference materials

Each CD-ROM drive for a personal computer (PC) may be characterized according
to the following:


      drive specifications
      formats the drive can read
      interface the drive requires to connect the computer


Drive formats
The data on compact discs need to be organized if the CD-ROM drive and
computer are to make sense of the data. The data are therefore encoded to
conform to certain standards. Although advanced CD-ROM standards are still
evolving, most drives today comply with earlier CD-ROM formats.




Interfaces
The CD-ROM interface is the physical connection of the drive to the PC's
expansion bus. The three typical interfaces are SCSI Standard, SCSI-2, and ASPI,
and nonstandard SCSI.




SCSI standard interfaces
Small Computer System Interface (SCSI) refers to a group of adapter cards that
conform to a set of common commands. These adapter cards allow a chain of
devices to be strung from a single adapter. Consequently, SCSI interfaces are
preferred for connecting a CD-ROM drive to a personal computer.




SCSI-2 and ASPI interfaces

SCSI-2 and Advanced SCSI Programming Interfaces (ASPI) take into account rapid
enhancements of computer interface technology. SCSI-2 incorporates several
enhancements, including greater data throughput and improved read and write
technologies. ASPI provides a standard software interface to the host adapter
hardware.



              TABLE 3. MULTIMEDIA STORAGE REQUIREMENTS



     One Minute Of...                      Storage Space Required



       audio, mono                               700 kilobytes



       audio, stereo                       more than 1.5 megabytes



         animation                           2.5 to 5.5 megabytes



            video                      20 to 30 megabytes, compressed
Nonstandard SCSI interfaces
Nonstandard SCSI interfaces may not accept installation of multiple SCSI devices;
in cases where this is not a problem, they may prove acceptable.




Read more: http://science.jrank.org/pages/1650/Compact-
Disc.html#ixzz0QSxK0OMq

				
DOCUMENT INFO
Shared By:
Stats:
views:26
posted:7/9/2010
language:English
pages:4