The ISAPI Standard and Perl Page 2

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Essentially, these APIs allow programmers to write hooks into the various stages of Web server processing. These hooks are typically program modules that do things like authenticate a user, but they can also be programmed to be a full-blown application. In the case of ISAPI Perl, Perl itself is embedded into the Web server using the ISAPI interface.

The difference between ISAPI and CGI is that ISAPI programs remain loaded in the Web server memory after an ISAPI program has first been loaded in memory. Thus, ISAPI programs tend to be much faster than CGI programs that are started and cleaned up for each and every Web application request from the user's Web browser.