Installing Windows In Legacy Mode

K I have a bit of a conundrum here, and I'm hoping you all can set me straight. I'm trying to reinstall Win 10 x64 on a Dell Alienware desktop. I have Win 10 on a bootable USB, but when I'm in UEFI mode, it won't recognize it. If I switch to Legacy mode in setup, it picks up the drive fine, gets me into Windows Setup, but then wont let me install, because it's not GPT. Even when I delete the partitions, and try to reformat, no dice. I've read a bunch of stuff online, but can't seem to find a clear explanation. It doesn't make sense to me that Windows wouldn't be more compatible with UEFI systems, as they're the norm now. How are you supposed to install Windows in UEFI mode, if it won't recognize external devices (i.e USB drives)?

 

UEFI Boot and a GPT disk require an EFI Boot partition which apparently you deleted.

In order to install Windows 10 on my Dell Inspiron 15-5555, I had to switch to Legacy Boot then use MiniTool Partition Wizard's bootable CD to delete all partitions and re-initialize the disk as MBR.

I, then, had to re-install the OEM Windows 8.1 Core because of the UEFI embedded Product Key (I could not install Windows 8.1 Pro). I was then able to create partitions and install Windows 7 Ultimate to one partition and Windows 10 Pro to another partition and I multi-boot with Legacy boot and MBR.

I don't know how large your internal hard drive/SSD is but, if it's 2 TB or smaller, MBR should work fine. Of course, you'll be limited to a maximum of 4 partitions.

 

I did mine almost the same as mdonah says.
GPT only allows 4 partition (Windows 10 creates another one, in installation, for its own use ).
I had a 1tb hard drive spare, so, I put it in a small external enclosure, and using Partition Wizard, I formatted it, then created 3 partitions, increasing the size in each, to accommodate more, for Windows 7, in legacy mode, ten, Windows 8.1 in legacy mode, then just installed my Windows 10, in that order.
I have yet to test Partition Wizard again to see if after that I could create another partition for data, as a 4th (although I should say 5th Partition)-I have read that it can, but when I put that hard drive back in, before I read that it was possible to create another partition with Partition Wizard, it said it could not read the file system, or, something similar (not a recognised system) However that was using a caddy, connected to my original hard drive. It may be that Partition Wizard's ability to "over-rule" Windows 10 , and its GPT limitation was created in the later version-I will let you know on that one. It may be that I will have to try that with Partition Wizard installed on that drive, and not in an external enclosure.

 

It seems pretty crazy to me that a UEFI enabled BIOS is unable to recognize a flash drive, and the only way to install it is by switching to Legacy.... Am I missing something here?

 

No. UEFI is designed to be much more secure than BIOS so, it will only allow booting from the internal HDD/SSD or the CD/DVD drive (Secure Boot). However, my Inspiron wouldn't boot to the optical drive even after changing boot order. So, I had to switch to Legacy and change boot order.

Then, I tried to install Windows 8.1 Pro — no go with a GPT disk.

@baklogic ,

A GPT disk can have up to 128 partitions. It's an MBR disk that's limited to four partitions.

 

UOTE="mdonah, post: 1994342, member: 303513"]No. UEFI is designed to be much more secure than BIOS so, it will only allow booting from the internal HDD/SSD or the CD/DVD drive (Secure Boot). However, my Inspiron wouldn't boot to the optical drive even after changing boot order. So, I had to switch to Legacy and change boot order.

Then, I tried to install Windows 8.1 Pro — no go with a GPT disk.

@baklogic ,

A GPT disk can have up to 128 partitions. It's an MBR disk that's limited to four partitions.[/QUOTE]

Yes, got that the wrong way around- probably because I had tried to use another partition once W10 was installed, and could not- got the message whilst I W10 on that drive, and it threw me, as I had setup the 4th partition for data, - GPT does make m have to think harder- I was lazy for years and used HyperOs to set my drives up , sometimes with 12 partitions to mess about with, so brain cells were asleep.
From what I have read, it seems that the usb drive needs to be set up as GPT, fat32, with something like rufas to work in gpt mode, with legacy support disabled to be seen when used at startup- but someone with more experience may have to explain that .

 

Would this help? From Dell.

-> http://www.dell.com/support/article...ndows-7--8--81-and-10-on-your-dell-pc?lang=EN

 

This would help to repair the EFI Bootloader if it's present. I believe the OP's was deleted. He's trying to re-install Windows 10 in UEFI Boot.

 

@jools1976 ,

I did some searching and found this. To install under UEFI, do what the tutorial says in the beginning about Secure Boot and have a look at Step 13.