Important Differences Between Version of IIS (4, 5, 5.1 and 6)

	IIS 4.0	IIS 5.0	IIS 5.1	IIS 6.0
Platform	NT4	Windows 2000	Windows XP Professional	Windows Server 2003 family
Architecture	32-bit	32-bit	32-bit and 64-bit	32-bit and 64-bit
Application process model	TCP/IP kernel MTX.exe	TCP/IP kernel DLLhost.exe (multiple DLL hosts in medium or high application isolation)	TCP/IP kernel DLLhost.exe (multiple DLL hosts in medium or high application isolation)	HTTP.sys kernel When IIS is running in IIS 5.0 isolation mode: Inetinfo.exe (in-proc processes) or DLLhost.exe (out-of-proc processes) When IIS is running in worker process isolation mode: W3Wp.exe (multiple worker processes) For more information on IIS isolation modes, see "Configuring Isolation Modes" in IIS Help, which is accessible from IIS Manager.
Metabase configuration	Binary	Binary	Binary	XML
Security	Windows authentication SSL	Windows authentication SSL Kerberos	Windows authentication SSL Kerberos Security wizard	Windows authentication SSL Kerberos Security wizard Passport support
Remote administration	HTMLA	HTMLA	No HTML Terminal Services	Remote Administration Tool (HTML) Web Server Appliance Kit (SAK). Terminal Services
Cluster support	In Windows NT 4.0	IIS clustering	Windows support	Windows support
WWW services	IIS on NT 4.0	Personal Web Manager on Windows 9x IIS on Windows 2000	IIS optionally on Windows XP Professional	IIS on a member of the Windows Server 2003 family