On 10/31/16 3:26 PM, Paul Koning wrote:
On Oct 31, 2016, at 2:58 PM, jim stephens <jwsm...@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.
Allison
