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I am using a MacBook pro running Catalina to create a bootable USB that I can use to install Windows 10 on another machine. Initially I formatted the USB as FAT32, but the Windows setup ISO includes a file that is greater than the max file size (4 GB).

I understand that ExFAT can handle files greater that 4 GB, but cannot be bootable. Therefore my plan was to partition the USB to have a FAT32 bootable partition, and an ExFAT partition. I would then load the ISO onto the second partition.

The problem I have now is that I cannot re-partition the USB drive. The option in the disk utility is greyed out. I erased it with a number of different formats, but to no avail. I also investigated command line options for eraseDisk but it doesn't seem to take a partition size parameter.

So, the question is can I create a bootable USB that will store a file greater than 4GB? How?

Secondly, if there is a better way to go about installing Windows 10 on a bare machine, please let me know.

DatsunBing
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  • Do either of these offer any clues: https://apple.stackexchange.com/questions/218818/how-to-format-multiple-exfat-partitions-on-usb-drive?rq=1 or https://apple.stackexchange.com/questions/240326/unable-to-erase-reformat-or-repartition-usb-drive?rq=1 ? – Monomeeth Oct 23 '19 at 23:54
  • Does bootable USB mean a flash drive, HDD, SSD or some other drive? I ask because Windows 10 generally only recognizes the first partition on USB flash drives. This is not true for HDDs or SSDs. – David Anderson Oct 24 '19 at 04:12

1 Answers1

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Your question lack sufficient information to properly answer. I will assume the machine where you wish to install Windows is a PC and not a Mac.

Certain Windows 10 ISO files can contain at least one file to large to be saved on a FAT32 formatted volume. However, when the same release of Windows 10 is saved to a USB flash drive by the Windows media creation tool, smaller files are substituted for the ones to large to fit on a FAT32 formatted volume.

One solution you be to install VirtualBox on you Mac. This is a free product. You can then use your Windows 10 ISO file to install Windows as a virtual machine. Once booted to Windows, you can download the free media create tool from Microsoft. This tool can be used to create a bootable Windows 10 installation USB flash drive.

Note: After installing VirtualBox, you will need to install the VirtualBox Extension Pack in order to access a physical flash drive from the virtual machine.

David Anderson
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