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I have an older iMac (Late 2012, A1418) that has a defective hard drive. I need to replace the drive and put in a fresh OS (Catalina).

I have the install media on a USB flash drive. My problem is that the drive needs to be formatted APFS and to do this I need another Mac running High Sierra which I don’t have.

Is there a way to format an external disk to APFS using a PC?

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    If at all possible replace the harddisk with an SSD, and not a mechanical one. The difference is very noticeable. – Thorbjørn Ravn Andersen Dec 25 '20 at 11:52
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To answer your question, there are good windows software package to read and write to APFS, however you don’t need this and none seem to allow partitioning or setup like you ask.

The stand alone installer knows enough to run Disk Utilty and prep a drive, so you don’t need a formatted drive. When you run the installer it will detect the bare drive and offer to erase, format, partition and install the OS.

Just boot up the installer and connect the new drive. It can be internally connected or externally connected and the installer will do the correct erase and format for you.

Your Mac might even be able to boot to internet recovery to get Disk Utility to partition the disk with zero local bootable OS or installers. Here is a step by step guide that Apple keeps updated for this procedure.

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  • I tried the installer but it won't recognize the disk format to write to it. It does see the disk, but refuses the install. I'll try Internet Recovery next. Thank you. – JCS Dec 26 '20 at 4:21
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If for some reason you are not able to format the drive though the OS installer:

  1. Replace the defective disk and connect the new disk to your Mac.

  2. Use macOS Internet Recovery to boot your Mac. Instructions here - How to Start Up a Mac in Internet Recovery Mode.

  3. Once it connects to the internet and boots into recovery, you can access Disk Utility from it.

  4. Use the Disk Utility to format the new drive.

  5. Then you can use your bootable flash drive to install macOS Catalina to the new drive. (If you don't have a bootable installer on your flash drive, then you will need to create that too from recovery - How to create a bootable installer for macOS.)

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  • Very good point for newer hardware. This won’t recovery boot, though. ifixit.com/Device/iMac_Intel_21.5%22_EMC_2544 – bmike Dec 25 '20 at 19:41
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    As the Fixit page says - Internet Recovery is only available on Apple computers made after 2009. If your computer was released in 2010 or 2011, you may need to update to the latest version of macOS and/or perform an EFI and SMC firmware upgrade to enable Internet Recovery. So there is a good chance that this particular model does indeed support Internet Recovery. – sfxedit Dec 25 '20 at 19:47
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    I should have said necessarily. Thanks for the correction! It’s certainly easier to internet boot on everything that supports it in my experience. – bmike Dec 25 '20 at 19:53

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