I own Acer M5 recently and it comes with 64-bit Windows 8. I need it to run Windows 7 x86. I changed the BIOS setting to boot under Legacy BOOT instead of UEFI mode.

I created my bootable USB using UltraISO. But when I select a partition it said "windows cannot be installed on this disk. The selected disk is of the GPT partition style".

A quick google search yeidls http://forum.acronis.com/forum/40223 and it seems like we can't run 32-bit. If I delete every partition will it work? Any alternative?


  • Bios cannot boot GPT partitions. Covert it to MBR or don't disable uEFi – Ramhound Sep 7 '13 at 22:56
  • @Ramhound thanks. Convert what to MBR? – CppLearner Sep 7 '13 at 23:04
  • The partition of course. If you enable UEFI you can install Windows 7 on a GPT partition, all you have to do, is disable Secure Boot which is a requirement( for you to be able to disable it ) on all Windows 8 machines with it. – Ramhound Sep 8 '13 at 2:35
  • 2
    The BIOS/GPT limitation is one of Windows, not one of BIOS. Also, a conversion to MBR involves converting the entire partition table, not just one partition. This has follow-on implications if dual-booting with Windows 8 is desired; see my answer for details. – Rod Smith Sep 8 '13 at 2:57

Your computer ships with a 64-bit EFI implementation. Such an EFI can boot only 64-bit OSes in EFI mode. Thus, to boot a 32-bit version of Windows, you must boot it in BIOS mode. This requires converting the partition table (not just a single partition; the entire partition table) from GUID Partition Table (GPT) form to Master Boot Record (MBR) form, since Microsoft has decided that it won't support booting in BIOS mode from GPT disks. Most disk partitioning tools can make this conversion in a destructive way (wiping out everything that's already on the disk), and a few can do so non-destructively. My own GPT fdisk (gdisk) is one of the latter. Note that MBR partitioning goes by a number of other names, such as "MS-DOS partitions" or "BIOS partitions." Thus, you might need to look for the right name, depending on what tool you use.

Note that even if you convert the partition table non-destructively, your existing Windows 8 will probably stop booting. (I haven't tried such a conversion myself, so I'm not 100% positive of that.) Essentially, you must boot all your Windows OSes in one mode (BIOS vs. EFI), at least if they're installed on one disk. If you want to dual-boot, this could be a problem, since given your stated goal, you may have to re-install Windows 8 in BIOS mode. This in turn will require access to a retail version of Windows 8, since the OEM restore tools will probably only restore in EFI mode.

This might be a bit easier if you're willing to run the 64-bit version of Windows 7. You could then install it in EFI mode rather than in BIOS mode, which would not require any partition table conversions and would enable dual-booting, if that's something you want to do.


I know this is way past the relevant time-frame, but let's set some things straight for the record.

  • @RodSmith is right in that tying BIOS firmware to MBR partitioned boot disk is a limitation introduced by Windows, not something inherent to BIOS/MBR. All modern versions of Fedora and Ubuntu work fine, in both x32 and x64 versions, with BIOS booting on GPT systems.

  • While I agree with @RodSmith that Windows 8 will stop booting on conversion from GPT to MBR, it should not be necessary to reinstall. A bootable DVD of Windows installation contains all the tools to fix it up, either automatically, or failing that, manually. Basically it involves writing MBR (using bootrec or bootsect), designating one system reserved partition (the erstwhile EFI System Partition will do), Volume Boot record (again using bootrec or bootsect), and then reintroducing bootmgr and BCD (using bcdboot). About half an hour overall.

  • It is not strictly true that Windows cannot boot from GPT on a BIOS system. Here is my technique for doing the "impossible" :

If you even have a small spare drive, you can boot Windows(either 32 or 64 bit) from GPT on BIOS. A floppy will do.

Boot into the Windows install/repair disc.

Create the system drive on the small disk/floppy, and use bcdboot to put your boot files on the the newly created drive on the small disk. Add a bootsector with bootsect. Change the {bootmgr} device to boot. Boot from small disk.

Steps are detailed here.


Faced a similar issue recently and this is what I did

Disabled UEFI. Switched to Legacy

During Windows 7 32 bit setup chose custom installation and deleted all existing partitions. Created a new partition from the unallocated space and windows setup allowed me to use that partition to install windows


The UEFI (Unified Extensible Firmware Interface) only support 64-bit Windows and GPT disk. You can't boot an 32-bit OS with a MBR disk on it. You need to install 64-bit Windows and GPT disk to boot in UEFI. For 32-bit and MBR, you must boot on Legacy mode.

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