Concerning operating systems, it is crucial to remember that Itaniums can only run operating systems compiled for the EPIC instruction set, whereas x64 processors will run operating systems compiled for them or for x86 processors.
For Itaniums, Microsoft has had Itanium versions of Windows XP Professional and Windows Server 2003 available to its customers for some time. The Itanium version of Windows XP Professional for the Itanium shipped with the 32-bit version of XP in August 2000, whereas the Itanium version of Windows Server 2003 shipped with its 32-bit counterpart in March 2003.
For x64s, if you have an x64 processor, then any 32-bit Windows operating system will boot on that system today. 64-bit versions of Windows XP Professional and Windows Server 2003 for the x64 will be released as part of the Windows Server 2003 Service Pack One release sometime in the first half of 2005. With the exception of Media Player, almost every feature will be implemented as a native 64-bit application.
My laptop is set up to dual-boot the 32-bit version of Windows XP Professional, and the 64-bit version of Windows Server 2003 Service Pack 1. If you have an x64 system too, and you are an MSDN Universal Subscriber, then you can download the beta versions of the x64 operating systems from the subscriber downloads site. You can find them under Windows Server 2003 in the content tree.
It is important to know, however, that all drivers have to be 64-bit when you are running a 64-bit operating system, so if you are using drivers other than those included in the operating system for any devices, then those devices will not work.
The operating systems for each processor family are compiled from the same code base, one for Windows XP and one for Windows Server 2003. However, not all of the features available in one version of the operating system are available on the others.
None of the 64-bit operating systems support these features that are available in the 32-bit versions:
· Microsoft DOS
· 16-bit applications
· The OS/2 subsystem
· The POSIX subsystem
· Certain effectively-obsolete transport protocols, like AppleTalk
There are a vast number of features that will be available in the x64 versions that are not available in the Itanium versions.
· Windows Firewall
· DVD video playback
· Movie Maker
· Windows Messenger
· MSN Internet Access
· ZIP Folders
· Home Networking
· Fast user switching
· Remote Assistance
· File and Settings Transfer Wizard
· Search Companion
· Power Management
· System Restore
So, compared to the Windows operating systems for the Itanium, which are somewhat bare-boned, the Windows operating systems for the x64 will be fully-featured.