Super User is a question and answer site for computer enthusiasts and power users. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I have a Windows 8 To Go Entreprise HDD, which boots both on BIOS and UEFI systems (I'm wondering how that's done, because I need that too).

Now, I see the HDD I use for that windows is an MBR HDD, it consist of a 350 MB FAT32 partition which holds the booting file to boot the second, NTFS partition which contains thw Windows 8 To Go operating system.

on the second partition I have placed a few ISO files under \partition2\ISO\.

for example:

Win8Install.ISO Win7Install.ISO HirenBootCD.ISO

when booting from BIOS into the system, and using EasyBCD to create startup entries for the ISO's, the ISO's boot fine, from BIOS.

But when going into UEFI another BCD table is used, so I re-added the ISO's to the UEFI selection, but when selecting the ISO boot created by EasyBCD on the UEFI boot selection, I get the following error:

enter image description here

How do I make UEFI boot ISO files or FAT32 partitions with grub4dos installed? They work fine on BIOS boot.

Seems windows To Go can boot from BOTH BIOS AND UEFI, on an MBR(!! [I have read UEFI can only boot from GPT, lies, lies everywhere]) disk. So this should be possible, please help me.

Edit: Activity Edit.

share|improve this question
Well, added a bounty and comment so --up--. – Gizmo Feb 26 '14 at 23:57
Does this have any relevance to your question? – Neolisk Feb 27 '14 at 2:24
Error 0xc000007b may relate to mismatch between 32- and 64-bit, so may be caused by 32-bit code trying to boot a 64-bit OS. Are you sure you are using grub4dos ? Its latest release dates from 2009 and knows nothing about UEFI. – harrymc Feb 27 '14 at 7:08
Another question: Why are you booting read-only ISO instead of VHD? Windows 7 & 8 have the ability to boot directly to VHD, no boot-manager required. – harrymc Feb 27 '14 at 11:17
and when I create, for example a windows 98 VHD, it CAN boot into it? (I mean, start the boot process). I have a 1TB portable HDD and I need to make it a rescue HDD for BIOS and UEFI – Gizmo Feb 27 '14 at 13:11
up vote 4 down vote accepted

Error 0xc000007b may relate to mismatch between 32- and 64-bit, so may be caused by 32-bit grub4dos trying to boot a 64-bit OS. The grub4dos latest release dates from 2009 and knows nothing about UEFI, so shouldn't be used.

You should probably start from scratch and use the tool UEFI MULTI.
The purpose of this tool is described as :

Tool to format USB-stick for Booting with Boot Manager Menu on BIOS or UEFI computer and Tool to make USB-Stick having two partitions - FAT32 Boot partition for WIM or ISO and NTFS System partition for VHD. Option to Install Grub4dos in MBR BootCode, which allows BIOS computer to boot directly from USB with Grub4dos Menu. Option to make Boot Manager and Grub4dos Menu on UFD to boot UEFI + BIOS directly from USB with Boot Manager Menu.

This link describes the procedure of how to create the USB disk.
The procedure is much too long to reproduce here.

Although this tool claims it can do what you want, I have no personal experience with it.

As regarding your question about how can one disk work for both BIOS and UEFI, this magic is probably achieved by using a Hybrid MBR, which is a format of the disk that looks as if it is both MBR and GPT. This is possible since GPT by design does not use the disk boot sector used by MBR. The size of a Hybrid MBR disk is limited to 2 TB, the maximum size of an MBR disk.

share|improve this answer
Grub4DOS uses BIOS routines and since UEFI dosn't provide BIOS routines it won't work with it. It's also 16bit code that uses real mode to address up to 1mb of memory not 32bit. – Brian Mar 3 '14 at 5:14
I think you mean 2 TB, not 2 GB, since that's the max for MBR disks. – IceMage Nov 9 '15 at 22:21
@IceMage: Thanks, I surely meant just that, but my fingers just didn't get the message. – harrymc Nov 9 '15 at 22:49

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .