Windows Server 2003 x64 Editions require server hardware that is based on the x64 platform. These servers feature AMD Opteron or Intel Xeon with EM64T or Intel Pentium 4 6xx series microprocessors. On the AMD side, Microsoft requires a 1.4 GHz or faster processor, while Intel users will need a 2.8 GHz Xeon or 3.2 GHz Pentium 4 with Hyper-Threading technology, or faster processor. However, Microsoft recommends faster Intel processors for the best experience: a 3.6 GHz Xeon or Pentium 4.
Microsoft doesn't want reviewers testing performance of these operating systems using pre-release code, which is fine because I don't typically run performance benchmarks anyway. (My testing was all performed with a single processor AMD-based system with a 2.2 GHz clock speed.) But the company tells me anecdotally that x64 has proven to be an amazing resilient architecture, offering full 32-bit application performance when running under a 64-bit operating system. This was a performance goal that eluded the company when working with the Itanium. "We wanted to eliminate any adoption barrier [for x64]," Iain McDonald, a Microsoft director of Windows Server program management, told me recently. "We think we nailed it."
But even for 32-bit applications, the x64 platform offers some advantages over x86 hardware. When you boot into a 64-bit Windows OS on x64 hardware, you get additional registers, and 32-bit applications each get a full 4 GB of address space, compared to 2 GB, typically, on a 32-bit box (previous 32-bit Windows client and server versions do support an optional 3 GB application address space mode).
Architectural improvements in the x64 chips, I'm told, also help with performance. The net effect is that 32-bit applications running in a 64-bit Windows version run at parity when compared to running in a 32-bit OS. In some cases, the code runs faster on x64, even dramatically faster. The reason, Microsoft says, is the additional resources a true x64 environment provides. The aforementioned application address space size is over 4,000 times larger than with x86 systems. The maximum physical memory is currently 8 times larger per server. The non-paged and pages memory pools are about 256 times larger on x64.
The nice thing about this performance boost is that it's not manufactured to meet a certain agenda. That is, Microsoft doesn't have to provide very specific benchmarks to prove its point. Instead, they've found Windows x64 to be faster running 32-bit code than 32-bit versions of Windows across the board. I'll provide the details when the final versions of the Windows Server 2003 x64 Editions ship.