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UEFI / BIOS GPT / MBR downgrading

Posted on 2014-04-17
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Last Modified: 2016-11-23
Trying to understand...
Questions...
1.  GPT formatted drives can only be used with UEFI...???
2.  MBR drives can have 1 partition...GPT has 3-4 partitions...One partition is for all the boot files...which means Bios in legacy mode cannot boot to GPT drive...am I correct...???
3.   On a working Win 8 box...if I turn Secure Boot off and UEFI to Legacy mode...Win 8 will NOT boot...???
4.   I have a Win 7 Pro image made from a MBR drive...can I install that image to downgrade from Win 8 to Win 7....???...Assuming Secure Boot is Off and UEFI is Legacy...???
5.  To install my image, will I have to convert the GPT drive to an MBR drive....???
6.  If #5 is "no"...If I delete all partitions on the GPT drive...will my image work...???

Here's my issue...

Company bought about 6 Dell 660s...couple had Win 7, rest have Win 8...We tried Win 8, We don't like it and boss says convert the 4 Win 8 boxes back to Win 7...

So in UEFI I turn UEFI to Legacy, and Secure Boot off...then I get "no boot drive selected"...

I CAN boot off my bootable Image CD...

Before I go any further, I just want to make sure I understand what's going on...

Many thanks
Steve
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Question by:stevem5000
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by:rindi
ID: 40007017
1. --> No. GPT drives can also be used on PC's with conventional BIOS. But M$ OS's would need an UEFI BIOS if you want to boot from a GPT disk. As long as you are booting your M$ OS from an MBR disk, you can still have a GPT disk as data or 2nd disk without the need for an UEFI BIOS. Linux can also boot from GPT disks even if the BIOS isn't UEFI.

2.--> No. MBR disks can have a maximum of 4 primary partitions. If 4 partitions isn't enough for a disk, you can make one of those partitions an extended partition. Within that extended partition you can create further logical partitions.

GPT disks can have more than 4 primary partitions, and support for extended partitions have been removed, as they aren't necessary anymore.

3.--> If your OS is installed to a GPT disk, then yes, it is true. If it is installed to an MBR disk, I believe it should still boot. But as I don't have a PC with UEFI BIOS available, I don't know.

4.--> That should work after you have converted the disk to MBR. Some imaging backup programs like those from paragon as far as I know have an option so you can restore an MBR image to a GPT disk. But booting would then only work if your Windows 7 OS is 64 bit. M$ OS's that are only 32 bit can only boot from an MBR disk, whether you BIOS is UEFI or conventional. Personally I'd remove the disk with Windows 8 on it from the PC and just install a fresh one for Windows 7. That way can return easily to the original OS should you need to. Besides, disks aren't that expensive.

5.--> answered in 4.

6.--> You don't have to delete any partitions. When you change a disk from GPT to MBR, it is initialized with a new partition table, and everything else that was previously on the disk is removed.
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by:stevem5000
ID: 40007056
Thanks Rindi...
One follow up question of #4....

You say...:"That should work after you have converted the disk to MBR."

So...how do I convert from GPT to MBR...???

I assume with a normal Win 7 install...I would delete all the GPT partitions, then create the partition(s) for Win 7...The single partition plus the little 100Mb paritition that comes along...
Then Reformat....That should put me back to MBR...

I don;t have that "partition delete and reformat" option with an image...

So....If I understand you correctly...I need to convert the GPT to MBR disk...using some available utility...???

Thanks again...
Steve
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Accepted Solution

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rindi earned 500 total points
ID: 40007093
Partitioning tools can initialize disks to either GPT or MBR (as I mentioned above you don't need to manually delete the partitions, as the initialization removes everything anyway). Diskpart, which is the utility that comes with windows, you could issue the following commands:

select disk 0
convert mbr

You can start diskpart from a Windows installation DVD for example by pressing shift+f10 when you reach the install to section (maybe even earlier), which starts a cmd prompt, and then just enter diskpart.

But as I mentioned above, it is probably easier to just replace the disks with new ones and then install Windows 7. Just make sure the new disks aren't larger than 2 TB (smaller is cheaper anyway, and in my point of view there is no reason yet to have such large disks anyway).
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by:stevem5000
ID: 40007140
Ok...Got it...!!!
Thanks again...
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