1 Dec
2011
1 Dec
'11
11:53 a.m.
On 2011 Nov 30, at 12:27 PM, Tony Duell wrote:
Not really. The pulses or flux transitions from the disk are in
discrete time slots relative to each other, albeit with some
fluctuation due to physical reality, but that fluctuation is not part
of the intended information content.
It is not like pulse-position-modulation or pulse-width-modulation
where the intended information is represented by a continuous value
('analog') of the time between two events (edges).
The disc-ferret/cat-weasel/etc. could be said to do a digitally-
sampled-analog-interpretation of those discrete time slots for the
sake of helping with data interpretation and recovery.
MFM drives are
not portable across controller models. And at least
sometimes, they're not even portable across examples of a given
model of
controller. Remember that the _analog_ waveform is passed up the
cable
to the controller, where the discriminator turns it back into bits.
Actually, it's analogue in the time domain , but only 2 voltage levels.
The circuitry tconvert the signal from the read head
toa digital
signal
is in the drive (the read amplifier, comparator, monostable, etc).
What
uou get at the interface conenctor is a stram of pulses, the leading
edges of which correspond to magnetic transitions on the disk. The
controller has to covert those pulses into parallel words, recognise
sector markers, and the like.
When writign, it's muchte same dviision. The controller takes words
from
the host system and serialises them. It also controls when to start/
stop
writing on the disk. The interface, again, is a digital pulse
stream, the
conversion from that to the head drive signals is done in the drive.
-tony