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install.wim larger than 4 GB on FAT32: why it fails and how to fix it
By Festo Kasalu Magembe · Updated 26 October 2026 · Part of the bootable USB for Windows on Mac guide
You copy a Windows ISO's files to a FAT32 USB drive and Finder or the terminal stops with a file-too-large error, usually on sources/install.wim. This is a hard limit of the filesystem, not a bad drive or a bad download.
Why it happens
FAT32 stores file sizes in 32 bits, so no single file can exceed 4 GiB minus one byte (4,294,967,295 bytes). Current Windows ISOs often carry an install.wim bigger than that. The rest of the ISO fits easily; one file doesn't.
Why "just use exFAT" isn't the answer
exFAT has no 4 GB limit, but most PC firmware (UEFI) can only boot from FAT32 on the EFI system area. A drive that copies fine can still fail to boot, so you trade a visible error for a silent one.
The fix: split the image
A WIM image can be split into numbered parts that Windows Setup reads as one image. The parts are named install.swm, install2.swm, install3.swm, and so on, each under the FAT32 limit. Nothing is recompressed, so the content and the Windows editions inside stay exactly as Microsoft shipped them.
install.wim, it splits it for you into parts of about 4,000 MiB, copying the compressed data byte for byte and rewriting only the headers and lookup tables. You'll see a "Splitting install.wim" line in the log.Doing it by hand
On any OS, the open-source wimlib tool does the same job:
wimlib-imagex split install.wim install.swm 4000
Copy the resulting .swm files into sources/ on the FAT32 drive and don't copy the original install.wim.
Things to know
- This only applies to FAT32. If you choose exFAT in Ndaga Fijo, files are copied unsplit, and many PCs won't boot the result.
- Images using the compressed "ESD" layout (
install.esd) can't be split this way, and are normally already under 4 GB. - Windows Setup finds the parts by name, so keep them together in
sources/.