1 Dec
2011
1 Dec
'11
1:04 p.m.
On 2011 Dec 1, at 12:12 PM, David Riley wrote:
On Dec 1, 2011, at 2:53 PM, Brent Hilpert wrote:
(As others have mentioned (including Tony), it is quantized in
amplitude (to two states) by drive read circuitry.)
In time, it was quantized when it was recorded and retains that
quantisation when read (note I said discrete time slots relative to
each other).
You might also note the part of my message you cut in your reply:
"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."
One can do an analog assessment of a digital logic voltage level
(e.g. 3.00V vs 3.02V) but that doesn't make the signal analog.
While there is some room for a little looseness in phrasing when
dealing with (signals from) a physical medium, it's still a stretch
to call the disk signal 'analog in the time domain', esp. when the
phrase has a firmer meaning in other applications.
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).
I'm pretty sure what Tony meant was that it's coming off an analog
amplification chain that gives you flux transition outputs; it's
not quantized by any digital circuitry. Thus it's analog in the
time domain and not synchronous to any discrete clock. 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 The one thing you *do* need to be careful about is
that you
oversample enough that the time domain aliasing doesn't give you
wrong results (i.e. if your data rate is 30 MHz and your sampling
clock is 33 MHz, you will have problems).
If the sampling hardware is running at 100MHz, you should be fine.
- Dave