CDs are the actual Compact Disks that you place in the CD-ROM drive. CDs hold approximately 650 MB of information. However, you must have a "CD-ROM" drive to be able to see or use the contents of a CD. You will need a "recordable" CD-ROM drive if you want to record on a CD.
A compact disk (CD) is a plastic disk, coated with aluminum alloy. The "plastic" base is made of a polycarbonate wafer (if you want to know more, consult a chemical engineer). The CD is written to by a laser, and read by a laser. CDs are available in 63 and 74 minute versions.
4.72 inches (120 mm) in diameter, 1.2mm thick, and has a 15mm hole in the center for mounting in the drive. CD-ROM drives are rated in terms speed. The are single, 2, 4, 6, 8, 12, and even a 16 speed in was introduced in 1997.
A single speed CD-ROM drive was designed to transfer data at 150 KiloBytesPS (KBPS) per second. Each speed rating is a number times 150 kbps. So, a 2 speed should transfer data at a 300 KBPS, and a 10 speed should be 150 MBPS x 10 = 1,500 kbps. or about 1.5MBPS.
Access Time is another matter - typically 100 to 200 Milleseconds! Very slow, but the higher speed drives help overcome this through higher transfer rates.
CD-ROM interfaces are SCSI/ASPI (Advanced SCISI Programming Interface) and IDE/ATAPI (AT Attachment Packet Interface), and proprietary versions.
CD-ROM drives can be purchased in read-only versions, or in "write capable" versions. The cost is obviously different, but not unreasonable for a "write" capable drive. "Recordable" versions of CD-ROM drives costs in May 1997 vary between $450-950.00 (different manufacturers) for an internal and external drives. The CD's themselves are very inexpensive ($7.00 to $9.00).
Future purchases of CD-ROM drives should be for drives with speeds of 8x or higher. This is a recommendation of "PCNovice" publication.
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