Where’s my Mac BIOS? (How to get into OpenFirmware Easily)

A lot of people these days appear to be under the impression that Macs have a BIOS, which is unfortunate because they actually have something much better – Macs have OpenFirmware. This is true for G4 Mac Minis, PowerBooks, iBooks, iMacs, eMacs, and Dual G5s… I could go on and on.
I got most of this info from experience and the Apple Developper Connection – if you’re not a member yet, sign up, it’s free.

You can get into OpenFirmware using this key sequence:


In detail, this means using two hands, holding “command”, “option” and “f” on the left and “o” with your right hand. Do this while booting your computer and you well hear two chimes. At the end of the chimes you will be greeted with an

On my G4 Mac Mini, for example, I can hold down the power button for roughly 10 seconds and I will hear the chimes – this should work for iMacs as well.

The OpenFirmware prompt that looks like this:



Congratulations, you’ve accessed your “BIOS” you switcher!

Now that we’ve passed this glorious milestone, we have some work to do. After all you came here for a reason right? (and not just to click on the ads, wink-wink nudge-nudge)

Some useful commands that save me time and time again, and enable reparation of the G4 Mac Mini:

Boot your Apple computer using the default boot device:

0 > mac-boot

Boot your Mac using the inserted CDROM at the yaboot directory for linux CDs:

0 > boot cd:,\install\yaboot

To eject a CDROM from your Mac:

0 > eject cd

If you have any other OpenFirmware tips to share, feel free to comment!

Join the Conversation


  1. have you tried it yet, techman? If it’s an apple, and with how they’ve been fairly consistent over the years, I would guess so. It does with an iMac.

  2. The new Macs use EFI, and there is no built-in shell access to it yet.
    On the other hand, if you are interested in getting your feet wet with EFI on an Intel Apple Mac, you may want to checkout rEFIt which is like BootCamp, only it supports other operating systems as well.

    Otherwise, holding the eject key on the keyboard will work, so will holding the mouse button down during boot up. I have yet to get a disc stuck in newer Macs and not have either of these work – aside from the occasional drive failure.

  3. I was trying to install Leopard to my MacMini and things got funny. Now I could not get it started. Press the power button, it starts, sound and then truning wheel…and then it stops. I had my Tiger cd inside and couldn’t get out, the keyboard eject didn’t help, etc.
    Try and error I found above as well (accessing BIOS and ejecting). However, I still could not get it going?
    – how do you create a “start up” cd in Mac? ıs there such a thing?
    – what else could you suggest?
    Many thanks.

  4. Are you using a newer Intel-based Mac Mini by chance?
    In this case, try holding down the option key on your keyboard if it’s a Mac keyboard, otherwise, try the F12 key on your PC keyboard.

  5. I have two MacMinis home. Install of Leopard worked just fine on Intel with no problems. It is the powerpc one that got stuck like this.
    My problem in fact is now not getting cd out but somehow making MacMini start (boot).
    Above you have a comment about booting for Linux. How about for mac, t force it to cd boot?
    Believe “mac-boot” would take me to original setting which is hard drive and that somehow does not work.

  6. hi, i hve apple laptop macbook frm my friend(u.k).he gift me this macbook laptop without any dvds or cds.nw its start bt nt operating system windows vista start.

    Apple MacBook
    Model no: A1181

    after start show me messages

    windows failed to start. A recent hardware or software change might be the cause. To fix the problem:

    1.Insert your windows installation disc and restart your computer.
    2.choose your language setting, and then click “Next.”
    3.Click “Repair your computer.”

    If you do not have this disc, contact your system administrator or computer manufacturer for assistance.

    File: NETIO.SYS

    Status: 0xc0000098

    info: windows failed to load because a required file is missing,or corrupt.

    Plz help me how can i do start operating system windows vista.i cnt speak enough english. plz send me solutions in my email address.please…..help meeeeeeeeeeeeeeeeeeeeeeeeeee……………………….

  7. Sounds cool your Macs. I started from Dos on a 286 and taught myself
    up through to vista 64, putting together hundreds of mainboards, video cards, Cpu’s, memory, bios upgrades and drive combinations.
    Eventually settling on xp pro fine tuned like a stradaverus, rock solid no leaks
    back to redmond.
    What I’m getting at those who have not been down this path, and are using
    a playstation counterpart of a PC, have missed the thrill and satisfaction of
    the challenge of a complicated elecronic modular puzzle that is a PC,
    and that because it is so versatile, in the right hands can take you further
    into unknown realms, if you know how.
    Still respect your Macs. To me Mac’s are clostraphobic, only my opinion.

  8. CAM…

    U just fired an never ending war against Mac and PCs.
    The PC are called IBM clones and Mac clones

  9. Hey guys, I am trying to install Mac OS 10.5 by accessing the Openfirmware on an iMac with 1GHZ and 256MB of RAM but I keep getting this error “LORD-SIZE is too small” after typing: boot cd:, \install\yaboot

    What could be the problem? Thanks!

  10. i am also getting the same thing it keaps saying this error “LORD-SIZE is too small” after typing: boot cd:, \install\yaboot. plz HELP

  11. Hmm… and just *why* is OpenFirmware better?

    Is it more robust? I can’t tell from the few commands I’m seeing in this discourse.

    Is it easier than a BIOS? Doesn’t sound like it to me. From your four-key access (only *one* key for BIOS), to all your DOS-like commands (there’s a simple selection of screens in BIOS that cover all your hardware control needs), OpenFirmware looks like *more* work to me. It reminds me of the classic fdisk utilities, but without even getting a prompt with options!

    What happened to the “easier to use” chant I keep hearing about Macs? It’s looking more and more like a Steve Jobs version of a Jedi Mind Trick on all you Mac users to me. Just saying something is easier doesn’t always make it so… and for the record, my XP *never* crashes, so you can toss that rusty old chestnut in the trash bin also. But hey, keep paying the bigger dollars for the sexy-looking equipment, if that floats your boat.

  12. Ok, so I recently got my hands on a Power Mac G4 with no OS whatsoever. Ive been trying to get a copy of Mac OS 9 to boot from CD but it won’t for some reason. The only way I managed to get to Open Firmware was once when I mashed my keyboard. I would open it again but Im using a PC keyboard, which doesn’t have a Command key. Is there a different way?

  13. Is there any way to boot an operating system from a USB drive? Im trying to boot Backtrack 3 on a flash drive, will that work with mac’s version of BIOS?

  14. Hi can anyone help me ..

    I tried to install Windows 7 on my MacBook Aplle The 1181 and was not booting, however I downloaded EasyBCD and made some changes in startup and rebooted my computer, and start showed me the following message:

    windows boot manager

    windows failed to start. a recent hardware or software may be the cause. to correct the problem

    – Insert the Windows installation disc and restart your computer
    – Choose your language settings and click Next
    – Click Repair your computer

    If you do not have this disk contact your system administrator or computer manufacturer for help

    The windows boot configuration data file contains a valid entry hole

    Someone help me please because not estrar on Operating systems not enter, and do not know what to do …

  15. Hello every one !
    Dear freinds i can’t find my MAC OS BIOS. When i start my notebook that is MAC BOOK and press Command + Option + 0 + F at the same time. BUT it is not working. Please help me.
    The mobel No: A1342
    Thanks in advanced.

  16. ok heres whats up im so anti apple not even funny its a thingbthat mac is tue red headed step child anyways ok i saw imac looks like short circuit ypu know the movie or et anyways its imac g4 so how do i install a debian based distro by the way im sorry mac is not imprrssive at all i was doing all this stuff years ago by the way apple quit suing famly i know your dev team isnt on it stick to your pc base or you about tp sell your self short

  17. I would like to know why my mac g4 agp boots up in the “open firmware” environment? That is, when I turn on the mac, my auxiliary screen displays text and then at the bottom of the text instructs me to type in “mac-boot” if I wish to continue. I do not recall doing the cmd+opt+o+f open firmware command string thing. How is the world can I turn this feature off and just have my mac g4 boot up normally!!
    Thanks in advance in your assistance with this persistent problem.


  18. i have an ibook g3/600/12mb/20gb h.d./dvd, with an airport card, with mac os 9.2.2. I received this from a friend without any software. It was running ok, but i wanted to update the os 9.2 to something like a os 10.4! Well anyways in the pc it showed another listing for another os so i clicked on this and now on a restart of the ibook, all i get is a grey screen an the apple and a working type circle an also in top left corner some black area with some dos writing. There is no reset button on this unit! I guess my question, Is there any way i can get the harddrive to reckonize the orginal os and boot up normal again?- thk-u! any solution would be helpful! This is my 1st apple pc, so not know much of them, Is there a way 2 boot from last good known configuration or something similiar?

  19. One thing I have found is that getting someone to help a newbie with anything Mac computer is like trying to pull sharks teeth. It is dang near impossible. I am getting frustrated with Apple and Mac because of the lack of help anyone can find for using their products.
    I have an 8 core late 2008 Mac Pro Desktop with 16 Mb RAM running El Capitan OS X.
    I was following the Apple site’s instructions on installing Windows7 Ultimate 64bit OS using bootcamp and it started installing, but then cancelled install. When I tried to start it back up, it will not boot into either Mac OS X El Capitan or into the Windows7 optical disk in the SuperDrive. It goes to a black screen like the ms-dos windows pre-startup screen telling about a card that is installed in the machine and then goes to a black screen with a cursor. During startup, it will not let me use any of the commands that should be able to be used. I have tried many of the combinations of keystrokes that Apple says will allow me access to boot up, etc., and none of them work. What do I do? I would like to use both Mac OS X and Windows 7 Ultimate 64bit on the same machine if possible… or…
    Is it possible to reformat the startup harddrive in MS-DOS and simply install Windows 7 and forget about the Mac OS X which don’t seem to have any support from Apple or anywhere else, for that matter. [At least the Windows OS has people who can help, whether working for Microsoft or not].
    Thank you for your time and effort in this matter, if indeed you can help me solve this problem.

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