For Microsoft, support for UEFI means rigorous testing on a wide-ranging mix of UEFI implementations and hardware platforms. As we learned when the industry shifted to ACPI with Windows 2000, every major PC or server manufacturer has its own firmware implementation for its own unique hardware. Therefore, we can't test just one implementation on one type of hardware. But to date, no production-ready UEFI implementations are available. So Windows teams cannot complete the appropriate testing before Windows Vista is released. By the time Windows Server Longhorn is released, we expect sufficient UEFI implementations to be available for testing with a solid set of manufacturers' hardware platforms.
Microsoft is working closely with the Unified EFI Forum and industry partners to ensure that we can provide a high-quality, standards-based EFI solution that works across x86 and x64 hardware. As part of this effort, Microsoft is providing a "technology preview" of EFI in the Windows Vista Beta 2 release. This preview will allow our partners to begin testing their UEFI implementations.