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bootcamp format usb drive to Fat32 when it want to create a bootable flash but biggest file is more than 4G. I even change its format to exFat but bootcamp makes its format Fat32 again what should I do ? I know the problem is Fat32 and I tried to change it to ExFat but bootcamp in creating bootable flash change its format to Fat32 format again.

that file is install.wim > 4G

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  • Your question is not clear. The current version of Bootcamp fully supports Windows 8. There shouldn't be a single file on a Windows 8 installation media larger then 4GB.
    – Ramhound
    Commented Jul 31, 2013 at 17:07
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    Are you copying the files in the win8 install iso to the USB drive ot are you trying to copy the ISO file itself?
    – Hennes
    Commented Jul 31, 2013 at 17:08
  • NO, I am using bootcamp to create bootable USB , and bootcamp do that
    – Farzad Salimi Jazi
    Commented Jul 31, 2013 at 17:29
  • Is the Windows 8 image your using was created by Microsoft?
    – Ramhound
    Commented Jul 31, 2013 at 18:10
  • what do u mean ? how can install windows on my macbook retina ? bootcamp format the USB in Fat32
    – Farzad Salimi Jazi
    Commented Jul 31, 2013 at 19:11

2 Answers 2

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Here is the reason for the issue where the Boot Camp assistant says there is not enough space on the USB drive when there is!!

FAT doesn't accept the install.wim file as part of Windows 10 because it is larger than 4GB which is maximum size for single file on FAT file system.

To resolve this issue and successfully install Windows 10 on bootcamp on my Macbook pro, I did the following:

On Mac:

  • Using Disk Utility on Mac, Formatted USB drive with ExFat file system
  • Downloaded Windows Support software using Bootcamp assistant, saved to the newly created USB drive

On Windows PC:

  • Downloaded the W10 ISO mounted it and copied contents over to root of USB drive

On Mac again:

  • Ran Boot Camp assistant but only with the 3rd option ticked
  • Chose my partition size and ran BootCamp which installed via the ExFat install USB drive.
  • Success: Windows installed!
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TLDR: Reformat as NTFS rather than FAT.

Slightly longer:
FAT (FAT12, FAT16 or FAT32) does not support files larger then 4GiB. So you can not use FAT formatted filesystems to host files of 4GiB or larger. You will need to use another filesystem.

If you want to install windows that needs to be a filesystem which windows understands. Since windows natively only supports a few filesystems you are limited to things like FAT (<4GB), NTFS or iso9660 (read-only).

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    Dear Hennes : ExFat supported by windows too and I reformatted it to ExFat on my mac but every time I try to create bootable flash using bootcamp it return to Fat32 !!!
    – Farzad Salimi Jazi
    Commented Jul 31, 2013 at 17:22
  • Windows does not support booting to ExFat partitions.
    – Ramhound
    Commented Jul 31, 2013 at 18:05

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