replace efi firmware with old legacy bios?

Question

So I bought a new laptop with 64-bit windows 8 pre-installed, and in preparation for downgrading to win7 32-bit, i've been reading about EFI and MBR etc.. It seems like the firmware which boots disks on my pc is EFI. I think already know how to install windows 7 now (by converting gpt to mbr), but firstly, will it even boot if I set boot mode to csm? (The installation dvd seems to work so my guess is yes)

And now my main question is this: Is it possible to flash my firmware to a legacy bios-based one instead of efi?

Answer 1

UEFI is perfectly capable of booting BIOS-bootable operating systems, using the so called “Compatibility Support Module” (CSM), which emulates all the necessary stuff.

And no, you cannot simply flash whatever you like. The firmware/BIOS is created specifically for your device. Unless the manufacturer provides a legacy BIOS firmware (he won’t), you’re stuck with UEFI/CSM.

Windows is too dumb to BIOS-boot from GPT disks. So just fire up the command prompt with Shift+F10 (possible at any time in Windows Setup) and launch diskpart. Then:

• Find your disk’s number with list disk
• Select the correct disk with select disk 9, where 9 is your disk’s number.
• Wipe it using clean WARNING: This will remove all partitions on the selected disk instantly and without asking for confirmation!

After that, continue with the setup routine.

Answer 2

Daniel B's answer is correct, but I want to note a few points:

• IN THEORY, you could flash an old-style BIOS over an EFI. The trouble is that you'd need to develop this BIOS yourself. If you're into this sort of thing, you could look at CoreBoot with an open-source BIOS payload. This is way too much hassle for most people, though. I recommend it only if you're into tinkering at this level, with bonus motivation if your EFI implementation is really bad.
• Although most UEFIs provide a CSM, a few don't. I own a couple of machines that lack this feature (both with 32-bit EFIs). I fully expect this feature to start disappearing in the not-too-distant future.
• A 32-bit OS is difficult or impossible to boot (in EFI mode) on a 64-bit EFI, so if booting a 32-bit version of Windows is really a requirement, the need for a BIOS-mode boot is necessary for minusatwelfth's situation. OTOH, using a 32-bit OS on 64-bit hardware is not something I'd recommend in most situations, so I recommend reviewing that detail.
• Windows 7 is perfectly capable of installing in EFI mode. There are some issues with getting a standard installation disc to boot that way, but they can be overcome. (I don't have any URLs handy, but I'm sure a web search will turn them up.) Thus, doing a 64-bit EFI-mode installation of Windows 7 would probably work as well as a 32-bit BIOS mode installation, assuming the 32-bit part isn't necessary for some reason.