15 Sep
2009
15 Sep
'09
8:46 p.m.
cclist at sydex.com wrote:
M2FM recording is pretty easy--the rules are less
complicated than MFM; I suspect the
reason that it isn't used today is that it's inherently less reliable. For a
decent description of it,
see page 5 of the Shugard SA800/801 theory of operation manual on Bitsavers.
The issue is that while M2FM channel encoding is simple enough, there
isn't a *standard* for a floppy disk M2FM track format. Intel M2FM
floppy format is different from Texas Instruments TMS9909 M2FM floppy
format, etc. The marks, PLO sync fields, etc. are different. Also,
some of the systems that use M2FM actually use a *modified* M2FM channel
encoding, which arguably should be called M3FM but isn't.
Eric