30 Oct
2016
30 Oct
'16
5:47 a.m.
From: Don North <north at alum.mit.edu>
.. the hardware bootstrap reads track 1 sectors 1, 3,
5, 7
Ah, thanks for that. Starting to look at the code, I had missed the
interleave.
So does DEC do anything with track 0, or is it always just empty?
Noel
30 Oct
30 Oct
4:24 p.m.
On 10/30/2016 5:47 AM, Noel Chiappa wrote:
Track 0 is not used by standard DEC software, block zero of the device (boot
block)
starts at track 1 sector 1. Track 0 is not even accessible thru the standard
drivers.
Applies to both PDP-11 (eg, XXDP, RT11) and PDP-8 (OS8).
Maybe specific software that reads/writes disks in IBM exchange mode accesses
track 0, but I've never used such s/w and am only guessing.
From: Don
North <north at alum.mit.edu>
.. the hardware bootstrap reads track 1 sectors
1, 3, 5, 7
Ah, thanks for that. Starting to look at the code, I had missed the
interleave.
So does DEC do anything with track 0, or is it always just empty?
Noel
31 Oct
31 Oct
11:58 a.m.
On 10/30/2016 4:24 PM, Don North wrote:
On 10/30/2016 5:47 AM, Noel Chiappa wrote:
Track 0 is not used by standard DEC software, block zero of the device
(boot block)
starts at track 1 sector 1. Track 0 is not even accessible thru the
standard drivers.
Applies to both PDP-11 (eg, XXDP, RT11) and PDP-8 (OS8).
Maybe specific software that reads/writes disks in IBM exchange mode
accesses
track 0, but I've never used such s/w and am only guessing
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.
Thanks
Jim
From: Don
North <north at alum.mit.edu>
.. the hardware bootstrap reads track 1 sectors
1, 3, 5, 7
Ah, thanks for that. Starting to look at the code, I had missed the
interleave.
So does DEC do anything with track 0, or is it always just empty?
Noel
12:26 p.m.
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
12:41 p.m.
On 10/31/16 3:26 PM, Paul Koning wrote:
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
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
5:04 p.m.
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.
On a floppy?
It might not be relevant HERE, but SOME computers have a different
physical format on track 0 (such as systems that evolved from FM to MFM
and continued to have track 0 be single density)
Writing to track 0 could be hazardous to whatever is s'posed to be on
track 0.
5:33 p.m.
On 10/31/2016 12:41 PM, allison wrote:
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.
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.
>
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
and MMD80.
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.
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
12:40 p.m.
On 10/31/16 2:58 PM, jim stephens wrote:
On 10/30/2016 4:24 PM, Don North wrote:
Big difference between hard disk and floppy.
Floppy the track 0 is generally used for "system level" things like
microcode load or boot block.
DEC varied on hardware (system) and OS and drive(media) as to its use.
On 10/30/2016 5:47 AM, Noel Chiappa wrote:
Track 0 is not used by standard DEC software, block zero of the
device (boot block)
starts at track 1 sector 1. Track 0 is not even accessible thru the
standard drivers.
Applies to both PDP-11 (eg, XXDP, RT11) and PDP-8 (OS8).
Maybe specific software that reads/writes disks in IBM exchange mode
accesses
track 0, but I've never used such s/w and am only guessing
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.
From: Don
North <north at alum.mit.edu>
.. the hardware bootstrap reads track 1 sectors
1, 3, 5, 7
Ah, thanks for that. Starting to look at the code, I had missed the
interleave.
So does DEC do anything with track 0, or is it always just empty?
Noel
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.
Every system
that had a MFM drive could format all tracks and even
either enter the printed bad block list or recover it before format.
Most all could discover new bad blocks as well. The RQDX1/2/3 ca with
XXDP software and the controller in the Microvax2000
can as well. THe higher level interfaces like SCSI can if the drive
permits it or its terminated with a ADAPTEC or Xybec SCSI to
MFM or RLL controller. All pre-IDE PCs could as well (WD1002/3/4/5/6
controller with MFM or RLL drive).
Allison
Thanks
Jim
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ajp166＠verizon.net -
cisin＠xenosoft.com -
jnc＠mercury.lcs.mit.edu -
jwsmail＠jwsss.com -
north＠alum.mit.edu -
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