Note: This is not a duplicate of:
- Windows explorer displaying wrong free space
- Windows Server 2008 r2 reports wrong hard drive free space
- Windows 10 reporting wrong hard disk free space
- Drive Space Inconsistently reported
I was manually writing boot sector for my USB drive. And yes, it show up as FAT, but the total space was 10.1 MB, while HxD and Disk Management show as 3.77 GB.