For the first time ever, the latest version of Windows won't install on an Intel-based computer. MS and Intel have lost synchronisation, to the point where the latest beta of 64-bit Windows doesn't work on
on-sale machines housing the Nocona Xeon processor.

Instead, the publicly available beta version of Windows XP 64-Bit Edition for 64-Bit Extended Systems can only be installed on systems with AMD's Opteron and Athlon 64 processors, according to a Microsoft spokesman. During the operating system installation process, Windows checks to see whether or not it is being installed on an AMD system. If it is not, the software cannot be installed, the spokesman said. However, Intel compatibility is likely to be restored sometime next month, according to Microsoft.

Microsoft's developers "essentially required the AMD chips to work with the operating system, just simply because they hadn't tested with any other chips," he said. Independent hardware reviewer Andrew Miller highlighted the incompatibilities in his review of a new Nocona workstation, one of a very few Nocona reviews to make it onto the Web following the chip's release last week.

The public beta for 64-bit Extended Systems was released in September 2003, before Intel had announced its plans to release the Nocona core. It has not been updated since then, and Microsoft's engineers wanted to ensure the beta operating system provided the same customer experience on Intel's chip as it does for AMD's chip before certifying it for Intel's chips.

There are some small differences between the instruction sets used in the two chips. Intel, for example, does not support AMD's 3DNow graphics instructions. Intel uses hyper-threading technology in its Xeon processors, while AMD does not.

AMD also uses two instructions designed to improve Opteron's ability to quickly switch back and forth between applications. The additional instructions were added after AMD published its design papers that Intel used to create the architecture for the Nocona chip. The instructions don't increase performance to any significant degree that most users would notice, according to analysts.

Aside from a few discrepancies, the chips are largely compatible. But even if they use the same instruction set, the chips don't have to use the same method to tell the operating system what instructions are available, said Kevin Krewell, editor in chief of the Microprocessor Report.

For example, AMD's and Intel's 32-bit chips are compatible, but don't necessarily use the same code to let the operating system know what types of instructions are available, Krewell said. Right now, the beta version of the operating system is probably tuned to recognise only AMD's method of identifying its instructions, but it will be relatively easy for Microsoft to add support for Intel's code, he said.

Microsoft is working on a new public release of the 64-bit beta operating system, the company spokesman said, but customers who have access to Microsoft's Tech Beta program will be able to preview the 64-bit operating system on Intel-based workstations.

The Bank of New York, for example, was able to get a pre-release of the beta code, which it is using to test a statistical trading algorithm that it is running on Windows in 64-bit mode on Nocona workstations built by HP, said Joe Weisbord, chief technology officer of the bank's G-Trade Division. His developers are using build number 1184 of the Windows XP 64-bit Edition, he said.

A beta version of Windows compatible with Intel's 64-bit extensions technology is expected to be released by the end of next month, according to sources close to Microsoft. Intel is planning to introduce a server chipset for its Nocona Xeon processors in August, right around the time the new beta version is expected. The Microsoft spokesman declined to comment on the exact timing of the updated beta release.

Intel and Microsoft have promised that the final versions of both Windows XP and Windows Server 2003 for 64-bit extended systems will run on Xeon and Opteron servers without any hitches. The production version of the operating system is expected in the fourth quarter.