idea for a universal disk interface

[Chris Zach]

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
>>>
>>>
>