Looking for SMD drives (specific models)

jwsmobile jws at jwsss.com
Sun Apr 12 20:48:59 CDT 2015

On 4/12/2015 5:05 PM, Jules Richardson wrote:

(actually Josh wrote this)
> I have a few other SMD drives (just picked 'em up today, in fact) but
> they're newer (~825mb) and the Ridge disc utilities only support a small
> subset of drives (they do not support providing custom geometries, 
> because
> that would be *too easy*.) 
The larger drives have more bits / track than the ones you have in the 
list. I suspect the 825mb and so forth may have too high a bit frequency 
for the ECC or CRC generation hardware in the controller.

I don't recall the number of bits / track, but there were a couple of 
generations with about 20k / track, the 9766 was in that class. Then 
later there were drives which were twice that.

The part we used to compute CRC for our drive at the time could not 
handle the frequency of the 40k tracks.  And the parts for ECC were not 
mature to change to that technology, so we never supported the EMD (40k) 

I have a CDC 160mb MMD which is probably compatible with the system you 
have.  I believe the Ridge was out when we did our controllers.

As to Jules's other mention, about the parameters, CDC recorded a well 
documented block of data on the first track with flaw map information.  
There are no drive parameters for SMD.  We had a rom with a number of 
geometries, as well as some table with block capacities which were 
reported to the Reality OS for it to use the drive.  Our interface was 
at a block count level, not a CHS layout level.

The place to attack Ridge would be to look for the tables for the drives 
that Josh has in his list in the disk controller roms, and attempt to 
modify that table.  That would assume one could modify that table, and 
there no protection on the rom such as a checksum that would mess up if 
you diddled the table.


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