Microsoft has decided not to support the Extensible Firmware Interface (EFI) in its forthcoming Windows Vista operating system.

EFI replaces the Basic Input/Output System (Bios) that has been used for the past 20 years. Both technologies give a computer its first instructions when turned on, and allow the operating system to be loaded.

EFI, however, has an advantage over Bios in that it allows for shorter boot times and lets hardware vendors to create device drivers which are independent of operating systems.

Microsoft had initially said that it would support the technology for 64-bit systems, but decided to make the changes because there will be too few 64-bit processors in the market when Windows Vista ships later this year.

"A combination of factors changed our plans," Microsoft development manager Andrew Ritz said in a session at the Intel Developer Forum in San Francisco, according to APCmag.com. 

"The big one, in my opinion, was platform availability. With this huge move to 64-bit based platforms and for us to support it, we needed to see a large heterogeneous sample of 64-bit implementations out there for us to feel comfortable in supporting it."

Intel developed EFI and supports the technology in its chips. While Apple is using EFI in its Intel powered systems, Microsoft only supports it in its 64-bit version of Windows XP.

Microsoft has said in the past that it targets the operating system at PC enthusiasts and warned against its use in real production environments.

Microsoft's decision throws up a hurdle for Mac users who were hoping to load both Windows and OS X on their Intel Mac hardware. The Intel Macs rely on EFI and lack a Bios.

This so-called double booting would allow gaming enthusiasts to use Apple hardware to play PC games that are not available on the OS X platform.