NTFS, exFAT or FAT32, and the 4 GB limit that catches everyone
Which format for which drive, why a large file refuses to copy, and what you lose by choosing wrong.
The format of a drive decides more than which machines can read it. It decides whether a large file can be stored at all, whether permissions travel, and how resilient the drive is to being unplugged carelessly.
The four you will meet
| Format | Use it for | Watch out for |
|---|---|---|
| NTFS | Drives used only with Windows | Read only on macOS without extra software |
| exFAT | Drives shared between Windows and macOS | No journaling, so unplugging mid write is worse |
| FAT32 | Only when a device demands it | No file larger than 4 GB |
| ReFS | Specific server and Dev Drive uses | Not for general external drives |
The 4 GB limit
This is the single most common surprise on this page. A FAT32 volume cannot store any individual file larger than 4 GB, so a video export or a disk image fails to copy with a message that sounds like a permissions or space problem. The drive is not full and nothing is broken: the format cannot represent the file.
# What format is it?
Get-Volume | Select-Object DriveLetter, FileSystem, FileSystemLabel,
@{n='SizeGB';e={[math]::Round($_.Size/1GB)}},
@{n='FreeGB';e={[math]::Round($_.SizeRemaining/1GB)}}Choosing
- Only ever used with Windows: NTFS.
- Shared with a Mac: exFAT, and eject it properly every time.
- A camera, a car stereo, a TV: whatever it specifies, usually FAT32 or exFAT.
- A Windows backup target: NTFS, because backup needs its features.
Reformatting
Changing format erases the drive, so the process is copy off, reformat, copy back. Verify the copy by opening files from it before erasing anything, because a verified copy is the only thing that makes this safe.
The space that disappears
A drive formatted for Windows keeps hidden folders on it: a per drive Recycle Bin, System Volume Information and, on a drive used with a Mac, Apple's own metadata. That is why a drive reports more used space than the files you copied, covered in the per drive Recycle Bin.
Common questions
Why can I not copy a large file to my USB drive?
Almost certainly because it is formatted FAT32, which cannot store any single file larger than 4 GB. Reformatting as exFAT or NTFS removes the limit.
Should I format an external drive as NTFS or exFAT?
NTFS if only Windows will use it, since it supports permissions and journaling. exFAT if a Mac needs to write to it, accepting that it has no journaling.
Does macOS read NTFS drives?
It reads them but cannot write to them without additional software. exFAT is the format to choose when both systems need to write.
Why does my external drive show less free space than expected?
Hidden folders: a per drive Recycle Bin holding deleted files, System Volume Information, and Apple metadata if it has been used with a Mac.