Rescuing a Mac using Windows

How to quickly create a macOS bootable USB on Windows

Here are the steps to create a macOS Sierra bootable USB media with GPT partition support on Windows 10 to rescue your Mac computer.

macOS bootable USB using Windows

Whether you’re a macOS Sierra user, or you run a different operating system, it’s just a matter of time until your computer won’t boot. There could be many reasons, such as file corruption or hardware failure, and when the unexpected happens, you can use a macOS bootable USB with the installation media to repair your Mac.

This is one of the main reasons why you should always consider on making a macOS bootable USB when your computer is working properly. However, if it happens that none of your devices (MacBook, MacBook Air, MacBook Pro, iMac, Mac Pro or Mac Mini) are not working when you need them the most, then you can use a Windows PC to rescue your Apple device. You can use a Windows 7/8.1, or a Windows 10 PC to quickly make a USB bootable installation media to reinstall macOS Sierra on your Mac.

In this guide, you’ll learn the steps to make a macOS Sierra bootable USB installation on Windows 10, which you can use to reinstall or upgrade Apple’s operating system.

Before proceeding

You’ll need a few things for this process, including:

  • A broken Mac computer with Mac OS X or macOS Sierra (version 10.12 or later).
  • A trial copy of the TransMac software.
  • One high quality USB flash drive with 16GB of storage.
  • A copy of Apple’s macOS (DMG file)

How to make a macOS bootable USB installation media

To create a bootable USB drive with the latest version of macOS, do the following:

  1. Download and install TransMac on your Windows PC. This is a paid software, but it gives you a 15-day trial, which is more than enough time. (If this works for you and want to support the developer, you can purchase the full version.)

  2. Connect the USB flash drive you want to use to fix your Mac. If you have any data on the USB, remember to make a backup, as everything on it will be erased.

  3. Right-click TransMac, and select Run as administrator.

  4. If you’re using the trial version, wait 15 seconds, and click Run.

    Run TransMac on Windows

  5. On the left, right-click the USB flash drive, select Format Disk for Mac. You want to do this before creating the bootable media because there is a good chance that the drive was formatted using a Windows device. If this is the case, chances are that it’s using a MBR partition, and the USB drive needs a GPT partition to work on a Mac.

    Format Disk for Mac using GPT partition

  6. On the warning message, click Yes to format the drive.

    TransMac format warning

  7. Enter a name for the drive, such as “macOS bootable USB” and click OK.

    Format USB for macOS with label

  8. Click Yes to confirm.

    TransMac overwrite warning

  9. If the formatting completed successfully, click OK to continue.

  10. Right-click the USB flash drive, and select Restore with Disk Image.

    TransMac Restore with Disk Image option

  11. On the warning message, click Yes to confirm the data on the USB drive will be erased.

    TransMac delete warning

  12. Click the browse button on the right, locate the .dmg file with the macOS installation files.

    Selecting dmg macOS file to create bootable USB drive

  13. Click Open.

  14. Click OK.

  15. Click Yes to create the macOS USB bootable media.

    TransMac create macOS USB bootable drive warning TransMac creating macOS bootable USB installation media on Windows

Once the process completes, you can now insert the USB flash drive on your Mac computer to install, reinstall, or upgrade the operating system to the latest version of macOS, which can be Sierra or later.

How to create a GPT partition on a USB flash drive

If the USB flash drive is not working using TransMac, it could be still a partition problem. In this case, you want to redo the entire process again, but this time use the following steps to use the Diskpart command-line utility on Windows to create the appropriate GPT partition.

  1. Open Command Prompt as an administrator.

  2. Type the diskpart command and press Enter.

  3. Enter the list disk command to view all drives connected to your computer and press Enter.

  4. Type the select disk command followed the number assigned for the USB flash drive (e.g., select disk 4), and press Enter.

  5. Enter the clean command and press Enter.

  6. Type the convert GPT command and press Enter.

  7. Enter the create partition primary command and press Enter to complete the process.

Once you formatted the USB flash drive to a GPT partition, you can use the instructions mentioned above to use TransMac to create a bootable media, but this time skip the steps 5 through 9, and continue on step 10.

After the process completes, which can take up to an hour, connect the USB flash drive and power on your Mac holding down the Option key, select the USB drive to beging the installation of macOS.

If you’re having problems creating the bootable media, you can get a USB flash drive that comes with macOS Sierra on it with link mentioned below. (I personally haven’t tried it, but it’s worth the try if nothing works.)

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