27 Jan
2016
27 Jan
'16
3:06 p.m.
On 01/27/2016 02:07 PM, Eric Smith wrote:
The double-density RX02 data fields are in a modifed
MFM, which is
what M2FM or MMFM stands for. It doesn't use the same encoding
rules as are most commonly used for M2FM, though.
...and that was exactly my objection. This becomes a case of the Monty
Python "Basingstoke in Westphalia" and "our Cole Porter". The RX02
MFM
(and I believe I touched on the rationale) may be "modified MFM", but
it's not modified in the standard (1,4) RLL encoding that the rest of
the world uses/used. I can conceivably change a couple of encodings for
FM, but that doesn't make it MFM. For example, not allowing 4
consecutive clock and data 1 bits in a row (I could, for example, leave
out a clock bit.). Come to think of it, that's exactly what standard
IBM 3740 address marks do, but nobody calls that "MFM".
If you insist that the 3740 format *defines* FM, then you're leaving out
a lot of recording formats that use (0,1) RLL, but not 3740 conventions.
Honestly, you DEC guys need to get out more.
--Chuck