I chose ESDI and SMD fundamentally because the interface is 100% digital
(e.g. the data/clock separator is in the drive itself). So I don't need
to do any oversampling.
TTFN - Guy
On 4/17/22 11:12, Paul Koning via cctalk wrote:
On Apr 17, 2022, at 1:28 PM, shadoooo via cctalk <cctalk@classiccmp.org> wrote:
hello,
there's much discussion about the right method to transfer data in and out.
Of course there are several methods, the right one must be carefully chosen
after some review of all the disk interfaces that must be supported. The idea
of having a copy of the whole disk in RAM is OK, assuming that a maximum size
of around 512MB is required, as the RAM is also needed for the OS, and for Zynq
maximum is 1GB.
For reading a disk, an attractive approach is to do a high speed analog capture
of the waveforms. That way you don't need a priori knowledge of the encoding,
and it also allows you to use sophisticated algorithms (DSP, digital filtering,
etc.) to recover marginal media. A number of old tape recovery projects have
used this approach. For disk you have to go faster if you use an existing
drive, but the numbers are perfectly manageable with modern hardware.
If you use this technique, you do generate a whole lot more data than the
formatted capacity of the drive; 10x to 100x or so. Throw in another order of
magnitude if you step across the surface in small increments to avoid having to
identify the track centerline in advance -- again, somewhat like the tape
recovery machines that use a 36 track head to read 7 or 9 or 10 track tapes.
Fred mentioned how life gets hard if you don't have a drive. I'm wondering how difficult
it would be to build a useable "spin table", basically an accurate spindle that
will accept the pack to be recovered and that will rotate at a modest speed, with a head
positioner that can accurately position a read head along the surface. One head would
suffice, RAMAC fashion. For slow rotation you'd want an MR head, and perhaps supplied
air to float the head off the surface. Perhaps a scheme like this with slow rotation
could allow for recovery much of the data on a platter that suffered a head crash,
because you could spin it slowly enough that either the head doesn't touch the scratched
areas, or touches it slowly enough that no further damage results.
paul
--
TTFN - Guy
