Technical information

ISAPI_Rewrite consists of four components – ISAPI filter, helper ISAPI extension, GUI Manager and MMC snap-in extension. ISAPI filter and extension are fast DLL modules written in pure C++. While installing ISAPI_Rewrite MMC snap-in will be registered automatically. ISAPI filter will be installed on a global level and you don't need to register it manually. ISAPI extension will be also installed and registered.

The ISAPI_Rewrite Manager utility can run ISAPI_Rewrite MMC snap-in on systems where MMC is not installed or inaccessible.

ISAPI_Rewrite Manager utility (Helicon Manager.exe) on Windows Vista and Windows Server 2008 systems require administrator priveleges to execute, because users with less priveleges don't have permissions to read from IIS metabase, which is required to display web sites configuration. You will be automatically prompted to login with administrator credentials if restricted user account is used to run ISAPI_Rewrite Manager.

ISAPI_Rewrite filter is fast enough not to worry about performance, unless your server is running under maximum load. Users will not find any difference in response time or CPU load, but the maximum server bandwidth may fall down a bit if large number of rules is used. So keep in mind that performance depends on a configuration settings you are using. It is not recommended to have more than 100 rules per web site. In most cases use of large number of rules can be avoided by utilizing RewriteMap functions.