HTTP Compression Methods and Files Used by IIS 5.0

By default, Internet Information Services (IIS) 5.0 uses the GZip and Deflate HTTP compression methods. Both compression methods are implemented through an ISAPI filter.

ISAPI Filter

HTTP compression is a subservice of IIS, which is handled through an ISAPI filter. Because this filter is installed at the WWW Service level, compression must be configured for the entire Web server. It cannot be configured for a specific Web site. The following two files handle this compression (located in the %WinDir%\System32\INETSERV folder):

• CompFilt.dll
• GZIP.dll

Compression Methods

• GZIP file format specification - RFC 1952
• DEFLATE Compressed Data Format Specification - RFC 1951

Note: To look up an RFC, see http://www.ietf.org (http://www.ietf.org)

For more information on enabling HTTP compression, review the Internet Information Services documentation.