I'm seeing tons of similar questions but never this scenario, or at least not with a solution...

I have an Acer Aspire laptop, no optical drive, with Windows 10 installed. BIOS is set to Legacy boot, and Windows works perfectly.

I downloaded Ubuntu 15.10 x64 and put it on a USB stick after using DISKPART to prepare the drive. I want to dual-boot Windows and Ubuntu.

When I boot from USB in Legacy, I get "Operating System Not Found". I've tried changing USB ports and drives, using both FAT32 and NTFS when formatting, never makes a difference.

I change BIOS to use UEFI instead of Legacy, and the USB drive boots perfectly and starts installation. In the installation process, it tells me that installing Ubuntu in UEFI will hose my other operating system. I think it'll let me do a full wipe of the hard disk and install, but I want to keep my Windows partition.

I'm assuming that if I can just get the USB drive to boot in Legacy mode, everything will be fine, but I can't figure out how to do that. Otherwise, if I could change my Windows partition so that it's UEFI instead of Legacy, I assume that would work too.

Any way you can think of to do either of these, or any other solution?


I wouldn't consider it a duplicate of the other question because I'm hoping to stay in Legacy mode so I can keep my Windows installation - that question is for a UEFI installation.

marked as duplicate by Eric Carvalho, David Foerster, RPiAwesomeness, Luís de Sousa, Mark Kirby Apr 1 '16 at 17:52

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • I have a similar system and installed Ubuntu Linux 15.10 along side Windows 10. You can choose the UEFI mode and at the time of install can go with the default option "Install Ubuntu alongside.." - this will create default /(root) and swap partition and then you can follow the on screen instructions. – Ashu Mar 25 '16 at 17:27
  • With Windows on Legacy and Ubuntu on UEFI, wouldn't there be a problem there? Wouldn't this stop me from being able to boot to Windows? That's what the warning message said - something to the effect of "if you continue, it will be difficult to reboot your machine in the other operating system" – Joe Enos Mar 25 '16 at 17:37
  • Both the O/S should be installed in the same mode. UEFI mode works fine for my Windows 10 and Ubuntu 15.10 – Ashu Mar 25 '16 at 17:41
  • Right, but my Windows is already in Legacy mode, so I'm trying to avoid having to wipe and reinstall Windows. – Joe Enos Mar 25 '16 at 17:42
  • I don't know the specific reasons why your Windows 10 is in legacy mode. May be you can ask the Acer Tech Support about it. You can try creating a recovery media of Windows 10 and then re-install it(Windows 10) in the UEFI mode(if this is new install plus data backup) and then try installing Ubuntu 15.10 in UEFI mode too. – Ashu Mar 25 '16 at 17:48

I'm not calling this a solution, but rather a working workaround - I used unetbootin instead of diskpart on the command line to create the bootable USB drive, and then it installed alongside Windows 10 as expected in Legacy mode, and now it dual-boots perfectly.

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