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When I use my laptop, I have no trouble at all accessing the BIOS and changing things like the boot order.

However I recently got an iMac and have found that not only do the usual keys not get me to the BIOS, but when I find one that gets me to a boot menu (holding option when booting up) it won't recognize my USB boot drive of Ubuntu!

How can I access the BIOS menu like I could in a PC?

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There is no BIOS on a Mac. It uses EFI, which can be configured from within OS X e.g. using bless from the command line.

You are able to boot from external USB drives that satisfy some requirements.

There are some key combinations that change the boot sequence, but there is no real boot menu.

Change the permanent preferred boot device in System Preferences on OS X or Boot Camp settings on Windows.

enter image description here

If you want more than what's available out of the box, you need to e.g. use rEFIt.

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  • @grawity What exactly was your edit referring to? Partially reverted because unclear (did you mean bless?), and conflict with an edit of mine.
    – Daniel Beck ♦
    Dec 30, 2011 at 22:01
  • I was adding a note about the ability to reconfigure EFI from the booted operating system ("EFI variables" on standard UEFI, although Apple obviously chose its own path), as opposed to BIOS which has to be managed through a pre-boot settings screen. This could be why Apple left out the pre-boot settings completely; it's all integrated.
    – u1686_grawity
    Dec 30, 2011 at 22:09
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    Actually newer Macs which can run windows do have BIOS. It's just that it's there only for compatibility with older windows versions that don't support UEFI and if I remember correctly, there's no way to access it.
    – AndrejaKo
    Dec 31, 2011 at 0:04
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    @AndrejaKo AFAIK, BIOS is only emulated on top of EFI in a minimal way to support Windows.
    – Daniel Beck ♦
    Dec 31, 2011 at 0:46
  • Could we update this answer from rEFIt to rEFInd?
    – CaldeiraG
    Nov 22, 2019 at 12:08

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