Short for Compact Disc-Read Only Memory, a CD-ROM (shown right) is an optical disc which contains audio or software data whose memory is read only. A CD-ROM Drive or optical drive
is the device used to read them. CD-ROM drives have speeds ranging
from 1x all the way up to 72x, meaning it reads the CD roughly 72 times
faster than the 1x version. As you would imagine, these drives are
capable playing audio CDs and reading data CDs. Below is a picture of
the front and back of a standard CD-ROM drive..
Interfaces
Below are the different interfaces that allow a CD-ROM and other disc drives to connect to a computer.
- IDE/ATA - One of the most commonly used interfaces for disc drives.
- Panasonic - Older proprietary interface.
- Parallel - Interface used with old external CD-ROM drives.
- PCMCIA (PC Card) - Interface sometimes used to connect external disc drives to laptop computers.
- SATA - Replacing IDE as the new standard to connect disc drives.
- SCSI - Another common interface used with disk and disc drives.
- USB - Interface most commonly used to connect external disc drives.
CD-ROM transfer speeds
Below is the standard transfer rates and access
times for CD-ROM drives. The below figures are averages you can expect
to find on each speed of CD-ROM drive..
| Drive speed | Transfer rate (Mbit/s) | Access time (ms) |
|---|---|---|
| Single speed (1x) | 1.2288 | 400 |
| Double speed (2x) | 2.4576 | 300 |
| Quad speed (4x) | 4.9152 | 150 |
| Six speed (6x) | 7.0653 | 150 |
| Eight speed (8x) | 9.8304 | 100 |
| Ten speed (10x) | 12.288 | 100 |
| Twelve speed (12x) | 14.7456 | 100 |
| Eighteen speed (18x) | 21.8343 | 90 |
| Twenty speed (20x) | up to 24.576 | 90 |
| Thirty-two speed (32x) | up to 39.3216 | 85 |
| Thirty-six speed (36x) | up to 44.2368 | 80 |
| Fifty-two speed (52x) | up to 63.8976 | 80 |
| Seventy-two speed (72x) | up to 88.4736 | 75 |
| CAV drives (12x - 24x) | 1,843,200 - 3,686,400 | 150-90 |