CD Drives: Storage on a Disc

There's a third type of disk that is now standard on personal computer systems. This disc is called a CD-ROM. (The initials stand for compact disc read-only memory.)

CD-ROMs look just like the compact discs you play on your audio system. They're also very similar in the way they store data (audio data in the case of regular CDs; computer data in the case of CD-ROMs).

Information on a CD-ROM is encoded in the form of microscopic pits (representing the 1s and 0s of computer binary language) below the disc's surface. The information is arranged in a series of tracks and sectors, and read via a drive that uses a consumer-grade laser. The laser beam follows the tracks of the disc and reads the pits, translating the data into a form your system can understand.

By the way, the ROM part of CD-ROM means that you can only read data from the disk; unlike normal hard disks and diskettes, you can't write new data to a standard CD-ROM. However, recordable (CD-R) and rewritable (CD-RW) drives are available that do let you write data to CD discs although they're a bit more expensive than standard read-only CD-ROM drives.

note

A drive that handles both recordable and rewritable discs is referred to as CD-R/RW.

Most CD-ROM (and DVD) problems have to do with dirty or scratched discs, or with dirty laser assemblies. Cleaning a disc is easy just use a soft cloth. If you have a scratch on a disc, you can try one of the so-called "CD scratch repair" kits sold at some stores, although I've found they really don't work that well; once a disc is scratched, the damage is generally permanent. (Which argues in favor of handling your discs as carefully as you do your audio CDs and only by the edges, never touching the surface of the disc itself.)

You should also avoid writing on the shiny side of disc, which is the side the laser reads. If you want to write on a disc, use a Sharpie on the label side. And don't use anything other than a Sharpie-like marker, as it could make the disc unusable.

tip

Many new drives combine normal CD-ROM, CD-R/RW, and DVD capabilities into a single unit.

If the lens that focuses the laser in your CD-ROM or DVD drive gets dirty, the laser can become unfocused and have difficulty reading the information from the disc. The solution to this problem is to use a commercial laser lens cleaner that you insert just like you do a CD-ROM disc.