Ubuntu – How does Ubuntu get away with reading FAT32

FAT has been expanded over time in two orthogonal ways:

• FAT pointer size -- FAT filesystem pointers come in 12-, 16-, and 32-bit sizes. The smaller sizes are useful on smaller media (like floppy disks) but impose media size limits. FAT32 is the least limiting in this respect; it can handle up to 2TiB partitions (or 16TiB for disks with 4KiB sectors). The FAT size is fixed when the filesystem is created, and it's not easily changed after the fact. Some tools report the FAT size of existing partitions, but others don't.
• Long filename support -- FAT was originally used by DOS (and variants of it by other OSes in the 1980s, and even in the late 1970s), and had a limit of 8-character filenames with an optional 3-character extension (so-called 8.3 filenames). With Windows 95, though, Microsoft introduced a way to store longer filenames on a FAT filesystem in a backwards-compatible way. This technique is called VFAT. Note that VFAT is not specified at filesystem-creation time; it's activated (or not) by the OS that accesses the filesystem. In Linux, this is done by specifying the msdos (8.3 filenames) or vfat (long filenames) filesystem type code to the mount command. A filesystem that's been used only by DOS can be accessed later as VFAT and long filenames added; or a disk that's been used with VFAT long filenames can be accessed without long filenames (but filenames will be shortened).

VFAT is compatible with any FAT pointer size, so you can have VFAT-12, VFAT-16, or VFAT-32. These terms are pretty rare, though; perhaps because the bit-depth is independent of the filename length, the bit-depth is often combined with "FAT" to identify that detail, whereas "VFAT" is generally used alone. All of this was pretty well-understood by computer-literate individuals in the mid-to-late 1990s, but the details have been forgotten (or never learned) since then.

This is a Windows issue, not an Ubuntu one. Nevertheless the reason is simple: Windows cannot see past the first partition on USB drives.

Here's how to do it correctly:

• backup the drive and erase it
• create a first partition (it doesn't need to be "on the left" of the drive, it just needs to be the first you create)
• format it as exFAT, NTFS or other convenient file system
• add the other Linux-only partitions

In this way, you get an advantage: Windows won't see the Linux partitions at all. I did this on a live USB key that needed a Windows part and it worked perfectly.