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I have a 4.04GB DMG file for Mac OS X 10.8 (Mountain Lion), which is being used for reinstalling the OS on my MacBook Pro.

However, the bootable USB needs a GPT (GUID-partition table) format. The only compatible format is FAT32, which supports a maximum of 4.00 GB per partition.

Is there any way to compress the DMG file to be smaller than 4GB, or booting from an ISO file?

I'm using Windows 7 on an HP Pavilion laptop. The .img file is 4.04 GB, and I need to copy that file to a USB stick that supports it. What format should I use in my 32 GB SanDisk USB stick while on the Windows 7 computer in order to read/write?

Alfredo Barreto
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  • What OS were you thinking of creating a bootable USB on? – Giacomo1968 Sep 11 '15 at 05:14
  • I'm creating the bootable USB on Windows 7. I have the .dmg file here. – Alfredo Barreto Sep 11 '15 at 05:26
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    possible duplicate of [Create a bootable USB drive from a DMG file on Windows](http://superuser.com/questions/383235/create-a-bootable-usb-drive-from-a-dmg-file-on-windows) – Giacomo1968 Sep 11 '15 at 05:27
  • Nope. The thing here is that the DMG file is 4.04 GB, and it needs to be smaller than 4.00 GB to be supported in a FAT32 USB stick. – Alfredo Barreto Sep 11 '15 at 05:30
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    The bootable USB needs to be GPT. Your concept it should be FAT32 makes no sense since FAT32 requires MBR. Please read that thread again. You can definitely do this, but you need to get over the FAT32 desire. – Giacomo1968 Sep 11 '15 at 05:32

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simply format your boot USB Stick with exFAT which can handle >4GB files fine and will be recognized by UEFI (and BIOS). just tested with and quite old MacBook Air

Falco Alexander
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  • macOS (or OS X, for that matter) support of exFAT is sketchy, at best, so that could be a problem down the road. If the drive has been formatted in Windows, it could work, or not, depending on the block size you use during formatting, and that's hit-or-miss: default cluster size in exFAT for a 32GB drive should be 32KB IF the drive is registered as being 32GB in capacity, not IF the available capacity is 32GB after reformatting/partitioning. If the drive's original capacity is over 32GB (and you plan on using only 32GB in a single partition), then default cluster size is 128KB. 1/2 –  Mar 30 '20 at 07:54
  • 2/2 bottom line is, Format your drive in a Mac if you plan to use it on a Mac and/or Windows. –  Mar 30 '20 at 07:55