Custom install.wim for UEFI and BIOS on same USB flash drive

Ztruker · 06 Aug 2019

Now that I have a working custom install.wim for UEFI and BIOS I'm wondering if there is a way to put both choices on one USB flash drive, via the Windows Setup Product selection window?

Custom install.wim for UEFI and BIOS on same USB flash drive-image.png

I'd like to be able to choose from a list something like:

Windows 10 Home (BIOS/MBR)
Windows 10 Home (UEFI/GPT)
Windows 10 Home (UEFI/CSM)

Could this be done with indexing?

If I can get three to work then I could get six to work and have Home and Pro on a single 64GB flash drive. I don't see it making things any easier for me at the shop but I think it would be fun to do and may help someone else at some point.

Bree · 06 Aug 2019

I don't think you can make it work like that. The standard Fat32 USB install media made by the MCT (or a Fat32 usb made from the ISO by the Diskpart/copy method) is capable of booting in either UEFI or Legacy Bios mode.

It is at boot time that the choice between legacy/MBR or UEFI/GPT is made. From that point on Setup can only install in the mode that you booted from the USB. If you boot in legacy mode it will use MBR, for UEFI it will be GPT. By the time you get to that OS choice menu in your screenshot it is too late to choose the install mode.

Ztruker · 06 Aug 2019

Bummer, seemed like a good idea. Thanks Bree.

So that is more a function of boot.wim then?

shockwaveriderz · 06 Aug 2019

depending on what your uefi bios settings is determines the install partition type: mbr or gpt.

If you have an old legacy only bios it will only install as a mbr partition.
if you have a uefi bios with CSM support enabled , it will install as a mbr partition
if you have a uefi bios with CSM support disabled, it will install as gpt partition
if you have a uefi bios with no CSM or legacy support it will install as gpt partition.

The win 10 install is smart enough to read the bios and then determine which partition type is suitable for the bios to be able to boot from.

This is not to say that you can't convert mbr to gpt or gpt to mbr afterwards using diskpart.

If you have a modern computer, using a modern OS like Win 10, gpt/ntfs is superior to mbr/ntfs and ntfs is superior to both exFAT and FAT32 in terms of speed and recoverability.

bro67 · 07 Aug 2019

Oh it can be done.
A BIOS to UEFI Transformation
Multi-boot UFD with Hi-Res Menus using Windows and Syslinux 6.xx

Ztruker · 07 Aug 2019

shockwaveriderz said:

depending on what your uefi bios settings is determines the install partition type: mbr or gpt.

If you have an old legacy only bios it will only install as a mbr partition.
if you have a uefi bios with CSM support enabled , it will install as a mbr partition
if you have a uefi bios with CSM support disabled, it will install as gpt partition
if you have a uefi bios with no CSM or legacy support it will install as gpt partition.

The win 10 install is smart enough to read the bios and then determine which partition type is suitable for the bios to be able to boot from.

This is not to say that you can't convert mbr to gpt or gpt to mbr afterwards using diskpart.

If you have a modern computer, using a modern OS like Win 10, gpt/ntfs is superior to mbr/ntfs and ntfs is superior to both exFAT and FAT32 in terms of speed and recoverability.

I was awar4e of all that. What I wasn't aware of was at what point the installer makes the decision as to what type of disk it wants, mbr or gpt. Now I know that it's done early, probably before the first install window is presented.

Thanks all.

Kyhi · 08 Aug 2019

It is done in PE - Disk Type depends on PE Boot type

Ztruker · 08 Aug 2019

What is PE? Looks like it means Preinstallation Environment but what is it, where is it, how does it fit into booting a customized install.wim from a USB flash drive that has autounattend.xml on it, one that worked okay previously on a different USB flash drive?