🚀 go-pugleaf

In article <1989Sep20.174011.20782@m2cs.uu.no>, tomas@m2cs.uu.no (Tomas Felner) writes:
> ONM07@DMSWWU1A.BITNET (Operator Julian) writes:
> >Is there any documentation about the bad sector list format used by
> >HDX? What is the meaning of the first 6 bytes? Any help appreciated!
> 
> I tried to figure out this myself some time ago, and even posted to the
> net, but no reply so far. However, I was able to decipher some of it
> myself. Here is my original posting from last march:
> 

The BSL is a place for bad sectors to be logged.  TOS doesn't use it.

----Warning! This is my opinion:-----

1. most disk interfaces use the Adaptec 4000a or 4070 controllers to
   connect mfm or rll drives.
2. These adapters will accept a list of BAD BITS as part of the low level
   format command.  This list is (i believe) standard, as my drives have
   such lists glued on them by the manufacturer.
3. After an Adaptec  controller has formatted the drive using this list
   all of the sectors IMPLIED by the bits disappear.  They do not appear
   in the BSL!.  The user only finds that the drive contains a few fewer 
   sectors that the full size.
   -- There is a SCSI command to adaptec to get this number.  Only the 
	BMS200 adapter can issue it however.
   -- Generally each bad bit area cost 1 sector.

4. HDX doesn't accept a bad bit list.  (I modified my version to use the
   info).
5. HDX and (Supra/ICD, I believe) do a function called loosely, finding
   bad blocks.
6. What they really do is first partition the disk into GEM partitions
   and then test the data area for bad blocks, marking them bad in the 
   FAT tables.
7. What happened to me was that the bad blocks were in the FAT and Root
   directory on one drive and this was a disaster.  This is why I changed
   HDX.

Howard C. Johnson
ATT Bell Labs
att!lzaz!hcj
hcj@lzaz.att.com