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When booting my mid 2014 13 inch Retina MacBook Pro, holding the option key to choose a startup disk doesn't work. I have just installed Windows 10 on an external SSD and the only way I can choose which to use as my startup disk is to change it from within whichever OS I am using, and my computer will boot into that OS until I change it again.

I tried resetting the NVRAM by pressing command+option+R+P on startup. All this did was boot into recovery mode. I want to be able to choose the startup disk by pressing option on startup but I don't know how to fix the problem I am having.

  • How did you create the external boot disk? Does it work on other Macs? – n1000 Jan 19 '17 at 9:51
  • I followed this guide to create the external boot disk. I haven't tried it on other macs. – Martin Harvey Jan 19 '17 at 12:23
  • If pressing Option during boot doesn't work, that strongly implies that your option key is faulty. Did you try the other option key as a check? – Zonker.in.Geneva Aug 6 '18 at 8:40
  • I've verified that both option keys are working while the computer is on and tried using both to select the startup disk. Unfortunately I still can't select the startup disk so the problem doesn't appear to be with the option key. – Martin Harvey Aug 7 '18 at 17:10
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So this issue is more common than you'd think. To me what you're describing sounds like the issue where the keyboard is not initializing on time to recognize the full key sequence you're holding down. If you're getting to the Recovery Partition by holding command, option, P and R that means that the system is either only recognizing the command and R keys at that time (which happens to be the exact sequence to get to the Recovery Partition), or at the very least not recognizing the option key.

First I would try resetting the SMC in case it's a System Management Controller issue. If you've never done one it's actually pretty easy, you just have to make sure it's charged over 10% first. Shut down your Mac. Disconnect the power source. Press Shift + Control + Option on the left side of the keyboard, then press the power button at the same time. Hold all 3 keys and the power button for 10 seconds and release. (I do recognize that if the 'option' key is the issue, this reset may fail as well.)

If this works you should now be able to reset the PRAM as well as access the startup disk screen.

If you still cannot reach the startup disk screen holding option, may I suggest testing with a usb-keyboard? (Not a permanent solution obviously but would give further insight as to what's going on.)

  • Thanks for the suggestion. I tried resetting the SMC but that doesn't fix the issue. I have tried with an external keyboard but that didn't change anything. – Martin Harvey Jan 19 '17 at 11:46
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Booting Windows from an external disk is not trivial. You need to closely follow the instructions given in a guide like this one to make an external disk bootable for Macs.

Disclaimer: I found the guide in this answer.

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