With the announcement of the first Intel based Macs yesterday, many users have rejoiced in being able to dual-boot both Mac OS X and Windows. Unfortunately, this is not the case; due to Apple's use of the extensible firmware interface (EFI) rather than BIOS, current Windows releases will not run on the systems.

On Tuesday at Macworld, Apple senior vice president of worldwide product marketing Phil Schiller said the company would not specifically block the use of Windows on Mac hardware. Instead, limitations in Windows itself will prevent its use on the new MacBook Pro laptop and iMac.

With the switch to Intel processors, Apple also moved from Open Firmware to EFI, which is an updated BIOS specification developed by Intel. Advanced features include the ability to boot into an EFI shell and run diagnostics and power up the CPU into a fully functional state immediately.


EFI also separates the control of devices from the operating system, meaning it can initialize hardware before loading the OS. This feature would allow for a system to connect to the Internet and download updated drivers before booting up.

Intel initially deployed EFI as part of its Itanium architecture. As such, Microsoft only included support for the BIOS replacement in its IA64 and later x64 operating systems. While Microsoft plans to add EFI support in 32-bit versions of Windows Vista, a final release isn't due until the end of the year.

Microsoft's 64-bit versions of Windows will also not work despite supporting EFI, because Apple's Intel platform is strictly 32-bit at the moment.

For its part, Microsoft encouraged Apple to build hardware compatible with Windows.

"We have an open specification and a process for certifying the hardware. We welcome all efforts in this area and we'd support Apple the same way we support every other PC manufacturer," a company spokesperson told BetaNews. "Anyone, including Apple, can purchase and re-sell Windows for use on their industry-standard hardware."