idea for a universal disk interface

[Douglas Taylor]

Once upon a time I used an Emulex QD21, but I sold it because the actual 
ESDI disks I had were a pain in the butt.  Always crashing.
I still have a Webster (quad board) SRQD something.
I think I had a Dilog board also.  It's been a while, probably 20 years.
Doug

On 4/18/2022 9:12 PM, Chris Zach via cctech wrote:
> Interesting, what kind of ESDI controllers do you have? They got 
> advanced features like cache, ordered seeks, and burst mode/block mode 
> DMA?
>
> C
>
>
> On 4/18/2022 6:09 PM, Douglas Taylor via cctech wrote:
>> 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
>>>>
>>>>
>>