[TUHS] Booting PDP-11's from RX02's

allison ajp166 at verizon.net
Mon Oct 31 14:41:48 CDT 2016

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 / sectors.
>> 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.
> 	paul
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.


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