[citation][nom]techguy378[/nom]A BIOS can't boot from anything but a disk with an MBR. Microsoft didn't do anything special in Windows to prevent you from booting from a GPT disk using a BIOS. The reason that Windows XP doesn't support hard disks greater than 2TB is because of the BIOS. If Windows XP supported EFI then it would have no problem with hard disks greater than 2TB.[/citation]
Wrong, a bios can't boot without a primary boot sector, it doesn't need an MBR. I've written boot loaders without MBR's, it works perfectly fine. No, they didn't do anything to prevent you from booting from a GPT disk, but they didn't do anything to support it either. If you say XP can't support it due to the bios, then how come linux supports it? Even without EFI it is supported in linux. If XP supported EFI they would have no choice but to support GPT, which is the actual reason it would work. There is nothing stopping them from adding in GPT support without EFI, since they are 2 seperate things. Even on microsoft's help site they say that you can use GPT without EFI, it's no friggin surprise, I don't know where everyone is getting this wrong information from (maybe news sites posting it all the time?). For some reason you guys cannot think and gather information on your own if it's not fed directly to you. I am telling you the straight up information, I have done a good amount of operating system development, from writing my own MBR that boots multiple OS's, to boot loaders, to kernel's, drivers, you name, i've probably worked on it. I know more about how BIOS's work and how booting a machine works than most people you will find on this site (especially if these responses are what people on this site think). I can write you a boot loader that doesn't have an MBR and send you an image of a hard drive to run in an x86 emulator like bochs, and prove that you can run stuff without a master boot record.
Also, if you think an MBR is required to boot, try putting a floppy in a drive (if you can find one). Low and behold, floppies don't have MBR, they are treated as a single partition. It is (was?) also common for USB drives to not have an MBR and be treated as a single partition, and it is still possible to boot from those as well.
http://www.microsoft.com/whdc/device/storage/gpt_faq.mspx - Specifically #5.
"5. Is EFI required for a GPT disk?
No. GPT disks are self-identifying. All the information needed to interpret the partitioning scheme of a GPT disk is completely contained in structures in specified locations on the physical media."
Even Microsoft states that you don't need EFI for GPT disks! They just chose not to support it in XP.