A data CD is a compact disk formatted to store files. The types of files typically stored on a data CD might include compressed zip files, word processing documents, spreadsheets, text files, graphics, QuickTime-style movie files, or MP3 music files.

A single data CD typically offers 680-700 megabytes (MB) of storage, providing a respectable chunk of space for building backups of everything from your MP3 libraries to your favorite programs. A data CD is also handy for storing sensitive files that are better kept off the computer’s hard drive where they could become subject to key loggers, snooping or virus corruption. This might include financial records, business records, tax or investment files, and so on.

Aside from archiving, a data CD can also be used to easily transfer large quantities of data, presentations or programs to another computer. A virtual supersized disk, the data CD is highly portable and fairly indestructible given a modicum of care in handling. Just four CDs provides over 2.5 gigabytes of storage power, making the data CD a convenient tool.

The data CD comes in two basic flavors: CD-R (recordable) and CD-RW (rewriteable). The difference is in the formatting and price. A CD-R is sometimes called a “write-once” CD because once something is recorded to it, it cannot be rewritten. Information can be added until the disk is full, but the CD is not rewriteable. The CD-R is less expensive than a CD-RW, and is used most often as an audio CD for burning music to the standard .cda format, which plays on any CD player.

A CD-RW can be written to many times, deleting and rewriting information. For this reason it is often called a data CD because it is handier for storing dynamic or changing information like backups and data files. However, these CDs are more expensive than the write-once CDs. For this reason – and because CDs hold so much data anyway -- many people use CD-Rs as data CDs, and simply buy new ones when they exhaust the space.

While the data CD certainly supplanted the humble floppy disk for portable storage and archiving, it too is being replaced by the memory stick. A memory stick is also rewriteable, even more portable, and comes in capacities far exceeding a data CD.