idea for a universal disk interface

[Douglas Taylor]

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
>>
>>