The source/vintage makes tham all probably
"1.2M" (anybody who wants to
argue the impreciseness of that designation can come up with a CONCISE
(not paragraph long) and unambiguous name for that type of drive)
5.25", 80 cylinder, 2 head, 360rpm, 500kbps data rate in MFM mode :-)
But I wil lagree that '1.2M' is common usage, and pretty unambiguous.
Similarly 1.44M for the 500kbps MFM data rate 3.5" drive (I do object to
a 'megabyte' being 10^3*2^10 bytes, but it's common usage...)
-tony