UPDATED 12/2/18: It doesn’t matter whether you’re a macOS Sierra or a Windows 10 user, it’s just a matter of time until your device refuses to boot, which could be for a number of reasons, including file corruption, hardware failure, buggy update, etc. If the unexpected happens with Apple computer, you can use a macOS bootable USB with the installation media to repair it.
This is one of the main reasons why you should always consider making a macOS bootable USB when your device 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 OS.
Before you dive into this guide, you’ll need a few things:
To create a bootable USB drive with the latest version of macOS, do the following:
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.)
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.
Right-click TransMac, and select Run as administrator.
If you’re using the trial version, wait 15 seconds, and click Run.
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.
On the warning message, click Yes to format the drive.
Enter a name for the drive, such as “macOS bootable USB” and click OK.
Click Yes to confirm.
If the formatting completed successfully, click OK to continue.
Right-click the USB flash drive, and select Restore with Disk Image.
On the warning message, click Yes to confirm the data on the USB drive will be erased.
Click the browse button on the right, locate the .dmg file with the macOS installation files.
Click Yes to create the macOS USB bootable media.
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.
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.
Open Command Prompt as an administrator.
diskpart command and press Enter.
list disk command to view all drives connected to your computer and press Enter.
select disk command followed the number assigned for the USB flash drive (e.g.,
select disk 4), and press Enter.
clean command and press Enter.
convert GPT command and press Enter.
create partition primarycommand 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 begin 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.)