Glossary >> I >> ISAPI >> What is ISAPI

What is ISAPI ISAPI stands for Internet Server Application Programming Interface. Basically, they are programs (non-cgi executables) written to interact & work with requets to a web server. There are 2 forms of ISAPI programs extensions and filters. ISAPI extensions: are directly invokable from a URL such as Assuming that you have set the proper permissions (permit Scripts and Executables and the IUSR_MachineName has the Execute NTFS permission) the dll will run. A good example of an isapi extension is FrontPage Server extensions. ISAPI Filters ISAPI filters are much more powerful as they are able to modify the incoming and outgoing data stream to and from IIS. They can be used to implement things such as custom logging, authentication, or to modify an IIS data stream. ISAPI filters also tend to run faster than the standard exe as they are optimized to run on your particular web server platform & once loaded into memory, the server doesn't need those extra cpu cycles to execute the filter again as it is already loaded into memory. Features implemented in ISAPI filters for IIS 5 include data compression, digest authentication, and URLScan. In IIS 6, all ISAPI filter run out of process. This will insulate the web server from a wayward ISAPI filter References ========== [1]