Professional Microsoft IIS 8

IIS 5.0 and 5.1

With the release of Windows 2000, IIS became integrated with the operating system. Version numbers reflected the operating system, and there were no upgrades to IIS available without upgrading the operating system. IIS 5.0 shipped with Windows 2000 Server versions and Windows 2000 Professional, and IIS version 5.1 shipped with Windows XP Professional, but not Windows XP Home Edition. For all essential functions, IIS 5.0 and IIS 5.1 are identical, differing only slightly as needed by the changes to the operating system.

With Windows 2000 and IIS 5.0, IIS became a service of the operating system, meant to be the base for other applications, especially for ASP applications. The IIS 5.0 architecture served static content, Internet Server Application Programming Interface (ISAPI) functions, or ASP scripts, with ASP script processing handed off to a script engine based on the file extension. Using file extensions to determine the program that handles the file has always been a common part of Windows functionality, and in the case of ASP processing, the speed of serving pages was increased by the automatic handoff of ASP scripts directly to the ASP engine, bypassing the static content handler. This architecture has endured in IIS to the current version.