Olivetti 3MB ST506-interface drive?

[Jules Richardson]

On 03/13/2016 03:12 PM, Chuck Guzis wrote:
> On 03/13/2016 12:38 PM, Jules Richardson wrote:
>
>> These 3MB ones were definitely Olivetti - this was from an ex-Acorn
>> employee who worked on the drive project. 3MB to 20MB seems a big
>> jump - but it makes me wonder if they were working with drives that
>> had three surfaces masked out due to manufacturing defects; one
>> surface would be 5MB, and going from 3MB per surface in a
>> pre-production drive to 5MB in
>
>
> Do you have a part number for the Olivetti drive?

No, unfortunately not, and the official service manual only mentions 10MB 
and 30MB drives (neither of which were Olivetti parts).

> I think that taking a
> 10MB drive and downgrading it to a 3MB one wouldn't be a paying venture.

AIUI, Olivetti only shipped these 3MB drives to Acorn while they were 
testing their Winchester unit - Acorn never used them elsewhere. I am 
curious if they ever saw production though.

Assuming for the moment that there were completely disabled surfaces 
involved due to too many defects (i.e. that this was a 2-platter drive with 
only one or maybe two active surfaces and the rest mapped out by the drive 
firmware), do you know how common a practice that was in the early days of 
ST506/412-type drives?

I've heard various stories of it happening much later with more modern IDE 
drives in the multi-GB range (e.g. a 20GB drive might be a 40GB 
single-platter drive with one surface that had completely failed QC), but I 
don't know if it was ever done in the ST506/412 era.

Jules