A traditional multivolume printed-on-paper compendium of information, specifically focussed on scientific and technical subjects. The most recent edition (copyright 2002) is available from the publisher at http://books.mcgraw-hill.com/cgi-bin/pbg/0079136656.html?id=zICnhjGN

The encyclopedia probably isn't heavily revised every year, although of course most-recent discoveries and techniques are likely added annually.

A CD-ROM version is also available from the publisher at http://books.mcgraw-hill.com/cgi-bin/pbg/0071341757.html

Note the indicated publication and copyright dates of the CD-ROM version are 1999 and 2000, respectively, indicating it is slightly "out of date".