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I've got a mid 2012 MacBook Pro (non-retina) with a removable HD (Machine A). I want to perform a clean install of OS X El Capitan 10.11 on the HD, for which I have an install USB stick made.

Normally to do this I would:

  1. Remove the HD from the Machine A.

  2. Put it in a HD enclosure.

  3. Plug the HD enclosure into another machine (Machine B).

  4. Run disk utility on Machine B to wipe the HD in the enclosure.

  5. Take the HD out of the enclosure and put it back into Machine A.

  6. Boot machine A into my installer USB and install OS X 10.11 from there.

I don't have a HD enclosure at hand and wondered if I can instead:

  1. Turn-off machine A.

  2. Link machine B and machine A by cable. (What cable spec?)

  3. Run disk utility on machine B to reformat the drive on Machine A.

  4. Perform task 6 from above.

Would that work? What cable should I use?

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4 Answers 4

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You don’t need to remove the HDD and no need for second Mac.

  1. Boot the MacBook Pro from the USB stick (that you made with OS X El Capitan 10.11)

  2. Using Disk Utilities in the Tools menu, you can reformat the hard drive as part of the installation process.

To boot using the USB, restart your MacBook and press and hold the Option key and Select the USB drive to boot.

Note: you are operating (using OS X) from the USB

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  • 3
    Just be aware that running MacOS from a USB is sloooow. But it works just fine.
    – gnasher729
    Commented Dec 9, 2018 at 13:52
  • USB 2 sticks are always slow. USB 3 is quite a bit better.
    – Dev
    Commented Dec 10, 2018 at 3:47
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There is no need for the USB stick, you can do a clean install from the recovery partition if it's available. Depending on the origin of the USB stick, it might even be a bad idea to use it at all.

Restart into recovery mode, delete the current installation and reinstall the operating system for the same result: https://support.apple.com/en-us/HT204904

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    Yes, while it is true one can use install from the recovery partition without a USB nonetheless, the User wants to install OS X El Capitan and the Mid 2012 MacBook Pro (non-Retina) shipped with Mac OS X 10.7.4 not OS X 10.11 and as such he cannot easily directly install OS X El Capitan 10.11 without using the USB Installer he already has that has OS X El Capitan 10.11 already on it. Using his existing USB Installer is the best and most recommended way to go under the circumstances!
    – user3439894
    Commented Dec 8, 2018 at 19:09
  • That is possible by using Internet Recovery, this installs the shipped OS. This 2012 model might have it.
    – John Keates
    Commented Dec 8, 2018 at 19:10
  • @JohnKeates A 2012 MacBook Pro can’t possibly have shipped with El Capitan, which was released in September 2015.
    – Mike Scott
    Commented Dec 8, 2018 at 20:27
  • @MikeScott I guess John means the 2012 model has Internet Recovery. “[installing OS X 10.11] is possible using IR, [recovery partition] installs the shipped OS”.
    – 11684
    Commented Dec 8, 2018 at 23:33
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    The OP already has already created a USB Installer with OS X El Capitan on it and it is senseless to not use it as one would then have to download another +5 GB, which depending on the bandwidth could take may hours. Not everyone has high bandwidth from their ISP. Yes while technically it can be done without using a USB Installer nonetheless it makes absolutely no sense whatsoever to do it any other way then using the already existing USB Installer with OS X El Capitan on it!
    – user3439894
    Commented Dec 9, 2018 at 12:38
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Can I re-format OS X drive without removing it from my MacBook Pro?

Yes.

You need not remove the hard drive from machine A or connect machine A to machine B to do this.

You simply need a bootable (USB) installer for OS X El Capitan 10.11. Once you have the bootable installer handy, simply leave the hard disk into machine A, plug-in the bootable USB installer, and boot off it.

Once booted, simply start Disk utility, erase the hard drive and perform fresh install of OS X El Capitan 10.11 on it.

You can find the instructions to create a bootable installer for OS X El Capitan 10.11 here:

To boot from the USB, simply restart your MacBook Pro with the installer USB drive plugged-in, and press & hold the Option key. You'll be prompted to select the boot media. Select the USB drive to boot.

For detailed instructions, refer to the Use Startup Manager section in the Apple Support article, How to select a different startup disk.

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The other answers describe the simplest and most straightforward way to do this.

However, for the sake of completeness, consider target disk mode.

Target disk mode allows you to boot your Mac into a state where it presents itself to other Macs as an external HD.

First, connect the two computers together with either USB C, Thunderbolt, or Firewire. Then, on the target computer, restart while holding down the T key.

The target Mac will boot to a screen with a Thunderbolt or Firewire symbol. It should appear as an external HD on the connected Mac.

See this Apple support article for many more details.

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