Hi,
1040ST lacked a floppy drive. 520STF and 1040STF had
floppy drives
(hence the 'F').
Here in the UK we got the "520STM" (no floppy, internal RF modulator) and
"1040STF" initially, and later the "520STFM"; I don't recall if
there was a
"1040STFM".
TTFN - Pete.