I've been involved with using computers for genealogy since 1985; at that time genealogical resources were limited to books, microfilms, microfiche, and original records with little or no electronic resources other than a handful of genealogy programs. While I believe books are still the most efficient way to disseminate genealogical information, CD-ROMs have given researchers the chance to purchase resources which previously were too expensive or out-of-print.

A CD-ROM (generally abbreviated to just CD-the name stands for Compact Disc: Read Only Memory) can hold as much information as several hundred floppy disks. CDs can contain 650 megabytes (MB) of information-that's roughly equivalent to 160,000 pages of text! Due to the nature of CDs and the CD-ROM drives, information can be read faster from a CD than from a floppy, making them an ideal media for storing and retrieving large amounts of data.

CDs you encounter that have been made commercially are read-only; that is, you cannot write data to them as you can a floppy disk. New rewritable CDs are available offering users the chance to use them as a small, portable, hard drive. The cost of writing information to a CD has fallen dramatically in the last few years as the price of the rewritable CD drives has dropped, making it a practical medium in which to publish a family tree, to sell society publications, or to simply serve as a storage facility for a researcher's genealogical database back-up files, photos, etc.

Types of Genealogical CDs

Genealogists encounter two basic types of genealogical CDs: those containing text, and those containing images. While many CDs are a combination of the two types, the CDs meant specifically for genealogists usually fall into one of these categories.