A CD-ROM is the name for a Compact Disk Read Only Memory. Compact disks are fairly common these days, both on computers and for playing music. Your question is about the computer CD that contains computer information. Like other forms of data storage, a CD-ROM needs to get it's original information from a computer.

The difference between a CD-ROM and, say, a floppy disk, is that a CD-ROM can not be erased, that's why it's called ROM. I looked up CD-ROM in the Compote's Mullet-media encyclopedia (on CD-ROM) and it stated:

The digitized data is fed to a laser that illuminates portions of a photosensitive material applied to a master disc. Whenever there is a pulse in the signal, the laser burns a small oval pit into the surface of the spinning disc. Eventually, an alternating pattern of pits and lands (flat areas) will remain on the master.

After a master disc has been inscribed, the spiral series of pits and lands is impressed on the molded plastic CD base. A layer of reflective aluminum is applied to the label side and topped by a protective layer of plastic. The side opposite the label contains all the information on a CD.

So, just like the old vinyl records, a "master" CD-ROM is used to press the copies. It makes the tiny pits that the laser will read as data.

I have included with my answer a CD-ROM that contains computer information. It's a very boring Government document, not exactly Sim City.

Excerpted from Compote's Interactive Encyclopedia. Copyright (C) 1994, 1995 Compote's NewMedia, Inc.

ˆHow do you make a Sim City CD-ROM?

Ryan, room 11, Mrs. Pottery