22 Dec
2005
22 Dec
'05
1:09 a.m.
Yes, most RLL drives can be formatted to lower
capacity and used on a MFM=20
controller, but some aren't reliable when used that way. I don't know which=
=20
are.
How can this be? With this sort of disk interface, the critical thing is
the timing between given edges (say rising edges) of the pulses on the
data line (the pulse width is not generally important). And I was under
the impressing that the set of times possible for the MFM interface was a
subset of the times for the RLL interface. And that a pulse stream from
the MFM interface was a possible pulse stream (albeit with a different
meaning) from the RLL interface too.
Sicne these ST506/ST412 drives are dumb devices (they don't try to
interpret the data pulses, they just record them and reproduce them), I
don't see how a drive can do RLL but not MFM.
-tony