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I know similar questions have been asked before across several sites, but the answers at least to me have been confusing and conflicting.

My understanding has always been that 64-bit Windows will create and use GPT disks just fine, but will not boot from them without a UEFI BIOS. Also my understanding WAS that 32-bit Windows could not use GPT at all and so is always restricted to 2.2TB disks, which was another reason to move to 64-bit on top of the 4GB memory limit.

But I have now read that this isn't correct: 32-bit Windows will create and use GPT disks just as 64-bit does. The only resriction is that you can't boot 32-bit Windows even if you DO have a UEFI BIOS? I don't think much of the literature has explained this well.

There are several tools floating around for creating virtual disks or 2.2+.8GB partition schemes and such for 32-bit systems. Why when it seems you can use GPT in 32-bit Windows anyway.

It also seems that people blame MS for lagging behind with respect to all of this: but it seems the issue is with BIOS manufactures not supporting UEFI rather than MS not supporting GPT...

Is my new understanding now correct?

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1 Answer 1

up vote 5 down vote accepted

You've got quite a few different technologies commingled there. I'll try to set out a few facts here:

  • Windows understands GPT just fine and is happy to use them regardless of 32-bit vs 64-bit.
  • Most BIOS systems do not understand GPT, and thus need a MBR block to boot. Some BIOS systems can boot GPT (I have one at home in fact).
  • EFI by spec supports booting from MBR or GPT.
  • Many EFI implementations have a BIOS emulation mode, this allows a EFI boot with BIOS compatibility for OSes that do not support booting from EFI. Support for this feature depends on your motherboard.
  • Windows 6.1 (7 and 2008R2) support booting from EFI only in 64-bit versions. Some other versions can be made to boot, but this is not recommended at the least.

Implications of the aforementioned:

  • Windows 7 32-bit needs to be booted from BIOS, which implies that it must be booted from MBR.
  • Windows 7 64-bit can be booted from BIOS/MBR, but can also boot from EFI/GPT.
  • Other configurations are possible but are not recommended and may be unstable.

Side note: There are a lot of minor improvements in switching to a 64-bit system. If you have the option always go 64-bit. There's really no excuse for doing otherwise, assuming you have any choice.

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Clearest explanation I have been given. Thanks. –  MrLane Apr 3 '12 at 2:18

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