If your Mac suddenly refuses to boot up properly, you might need bootable macOS install USB to make repairs. But how do you create such a disk if all you're left with is a Windows 10 computer? Fortunately, there's a great tool that you can use for free to create bootable macOS media on a USB drive in a Windows 10 environment. This article shows you how to download a macOS DMG file, format a USB drive using a GUID Partition Table, burn the DMG to the drive and boot your Mac from the USB. All the steps except the last one are done on a Windows 10 machine.
Jul 11, 2011 A DMG file is a disk image file. You first must have a virtual imaging interface such as Daemon Tools. You can then use this program to mount your DMG file or you can burn it to a disk! ImgBurn is a lightweight CD / DVD / HD DVD / Blu-ray burning application that everyone should have in their toolkit! It has several 'Modes', each one for performing a different task: Read - Read a disc to an image file; Build - Create an image file from files on your computer or network - or you can write the files directly to a disc.
Part 1: Download macOS or Mac OS X DMG File
The first step is to get the DMG disk image file for the version of macOS that you want. You can get a copy of the latest macOS version from Apple download portal or App Store here. There are also several other direct download sites that offer various versions of Mac OS X in DMG format rather than the standard APP format that runs on Mac. Since you're working in a Windows environment, you need the DMG rather than the APP file.
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Part 2: Format USB Drive to GPT
Mostly, the USB drive was formmated to FAT32 in default when being shipped out from the factory. However, FAT32 can be only used for installing OS with legacy BISO, which doesn't work for macOS. So the next step is to format your USB drive in the GPT partition style in order to burn installation files to the desired USB drive. You can do this in Command Prompt as admin. In elevated Command Prompt (Ctrl+Shift+Enter), input the following series of commands followed by Enter after each line:
Diskpart
List disk
Select Disk X (X stands for the USB drive name that appears after the previous command)
Clean
Convert GPT
Create partition primary
Part 3: Create Bootable macOS USB from Windows 10
You have now formatted the partition of USB drive. It's time to download TransMac for Windows. Although this is a premium software, you can use the initial free trial period to create a bootable macOS USB drive on Windows 10. After installing the application, follow the sequence of steps shown below:
Step 1: Right-click the icon and select Run as Administrator from the contextual menu. Choose Run when prompted.
Step 2: Insert your formatted USB drive, and you will be able to see it in the TransMac software on the left panel.
Step 3: Right-click the USB and select Restore with Disk Image in the contextual menu. Click Yes in the warning popup.
Step 4: You will see a window that says Restore Disk Image to Drive. Here, select your DMG file in the dropdown menu and click OK.
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Depending on the system configuration, this can take anywhere from a few minutes to a couple of hours. Once the progress bar is at 100%, a bootable USB is ready.
Part 4: Boot macOS Install USB on Mac
Now remove the USB drive and insert it into the Mac computer. To boot from the disk, you need to hold down the option key when you hear the boot chime. This will take you to the Startup Disk Manager, where you should be able to see the USB drive. It might have a different name, but as long as it is bootable, you'll be able to see it there. Once you select it, the computer will boot from the disk and the macOS installation will begin.
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Conclusion:
The whole process might look a bit complicated if this is your first time, but just follow the instructions in this article and you should be fine. That being said, you need to be careful when downloading the DMG file and formatting your USB drive. If you don't do these two steps correctly, the output drive from the TransMac software won't be bootable, which means you can't install macOS using it, and you may need to do the whole thing over again.