idea for a universal disk interface
Douglas Taylor
dj.taylor4 at comcast.net
Mon Apr 18 17:09:40 CDT 2022
Because of this I'm holding on to my DEC Qbus ESDI controllers!!! You
never know....
Doug
On 4/17/2022 4:35 PM, Guy Sotomayor via cctech wrote:
> 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 at 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
>>
>>
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