The story then goes on further: every NTFS volume contains a special file named `$UpCase` that has a uppercase mapping for all possible 16-bit words, resulting in an 128 KiB table. This approach has an upside for backward and forward compatibility... unless you eventually need a case mapping for non-BMP characters or complex mapping that expands to multiple characters.
NTFS is (usually) case preserving but not case-sensitive. So the OS needs to be able to tell whether EXAMPLE.TXT and example.txt are the "same" name, which means it needs case conversion.
Not everybody agrees about how this conversion should work. The most famous example is Turkish, but there are others. So there's an actual choice to make here.
If Windows baked this into the core OS, they might get pushback in countries where their (presumably American) defaults were culturally unacceptable.
If they made it configurable at the OS level, everything would seem fine until, say, a German tries to access a USB drive with files from a Turk on them and some files don't work correctly, or the disk just can't be mounted at all.
So, they have to bake it into each NTFS filesystem.
