[TUHS] Booting PDP-11's from RX02's
jwsmail at jwsss.com
Mon Oct 31 19:33:01 CDT 2016
On 10/31/2016 12:41 PM, allison wrote:
> On 10/31/16 3:26 PM, Paul Koning wrote:
>>> On Oct 31, 2016, at 2:58 PM, jim stephens <jwsmail at jwsss.com> wrote:
>>> If you cared about not erasing the drive manufacture's data on
>>> sealed media Winchester and the like you have to avoid any writes to
>>> cylinder 0 at all.
>>> The drive formatting software could read that cylinder track 0 for a
>>> defect map. Nothing to stop you from overwriting it, but you would
>>> then need to do a local media certification that is more complicated
>>> than just formatting the drive, and mapping out defective tracks /
>>> I never worked with a system that had a controller or software that
>>> could read the defect track, so don't know how that was used. Later
>>> drives with more intelligence in the drive are another matter, but
>>> in those cases, the hiding of the defect data can be a task assigned
>>> to that processor, and don't need magic handling of the addressing.
>> I haven't seen drives that put the defect data on track 0. DEC put
>> it at the very end of the drive (see DEC Std 144). And as I recall,
>> CDC did likewise in the 844 drives (RP04 lookalikes). As for software
>> using that data, RSTS certainly did.
CDC MMD and cmd put the map on cylinder 0. If you had a design that
could read the track zero info, you could auto configure between MMD 160
Having the defect info on the last cylinder would have worked in that
case, but in design meetings with the ANSI SCSI committee, the seek to a
maximum cylinder would have meant the controller would need to know that
in advance when powering up.
Having the info on cylinder 0 with the defect list would allow for auto
config. I don't know that it was used, but I don't recall any
discussions with the info on the last cylinder, though I'm sure the DEC
guys would have mentioned it were they in on the discussions.
> But its not done (defect mapping) on floppies. defects on floppies
> are a media or drive issue.
> Also drive that grind away track 000 usually have enough gunk on the
> head to take out other tracks.
Only talking about sealed media such ad MFM, SMD winchesters. I guess
it wasn't clear. Maybe the discussion about starting @ track 1 was
about floppies, and I missed that.
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