So my understanding is that Ubuntu desktop 13.04 ISO comes in two flavors:

  • 32-bit (supporting only legacy boot mode)
  • 64-bit (supporting only EFI boot)

Is this correct? What I want is a single bootable image that will boot on both my legacy computer and my newer computer. They both currently run 64-bit software, but I can't get the 64-bit image to boot on my older computer.

I don't really care if I run 32-bit or 64-bit Ubuntu, what I do care about is using the same USB stick for either computer. Is there an easy way to get the 64-bit image bootable in legacy boot mode for my older computer? Or is there an easy way to get the 32-bit image bootable under UEFI on my newer computer?

Or, if the 64-bit image should just work in legacy boot mode, please let me know.


  • How old is old computer. If later than Pentium M you do not have PAE issues. And if you have more than about 2GB of RAM the 64 bit version will give better performance. My 6 year old laptop with dual Intel process and 1.5GB of RAM runs the 12.04 64 bit version just fine if I do not try to load too many apps at once. – oldfred Aug 19 '13 at 4:34
  • I built it from premium parts in 2007. 4 GB RAM. Core 2 Duo. – Eddified Aug 20 '13 at 0:03

The 32-bit Ubuntu is BIOS (legacy) only, whereas the 64-bit Ubuntu supports both BIOS and EFI boot modes. Thus, the 64-bit image should work on your older computer, provided that computer has a 64-bit CPU. The x86-64 (aka AMD64, x64, or EM64T) architecture dates to 2003 (with AMD's Opteron line), but it started to become popular a couple of years after that. Even today, some computers still use 32-bit CPUs, although they're mostly low-end or embedded devices. Thus, without further details, it's unclear whether your older computer is 32- or 64-bit.

The 32-bit Ubuntu should run on 64-bit computers, including most EFI-based systems; however, to boot on an EFI-based computer, a BIOS-based OS (including standard 32-bit Ubuntu live CD/USB images) requires that the EFI have a feature known as the Compatibility Support Module (CSM), which is a BIOS-compatibility layer. Most modern EFIs have this feature, but it's often disabled by default, so you may need to enter your firmware setup utility to enable the CSM (aka "legacy mode" or "BIOS mode"). The details of how to do this vary wildly from one EFI to another, so it's impossible to give simple and accurate instructions for doing so that apply to all computers.

  • Thanks. I know for a fact both of my computers run 64-bit software. I think the difficulties booting have to do with a failing BIOS on the older computer. (There are other symptoms as well, besides failure to boot anything on USB media.) – Eddified Aug 20 '13 at 0:01
  • But still, this answer is exactly what I was looking for. +1! – Eddified Aug 20 '13 at 0:01

The 64-bit Ubuntu live USB disk will work even if you turn off UEFI. The 32-bit version of Ubuntu does not support UEFI. So, if you are not having trouble getting the older PC to work with the 32 bit version of the Ubuntu Live USB, you can get both computers to run it as long as you turn off UEFI on the newer machine.

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