Back in the day 5.25" disks were sometimes (or usually) laid out with sectors out of order, because CPUs were really slow and couldn't read the sectors as they came by and fdcs did not have a buffer to hold the sectors until the host requested them. So they would take 2 or 3 revolutions to read each side of the disk. Could it be you just start at 2 but there is a 1 later on?
DCN
On Wed, 12 Jan 2011, Ian Oliver wrote:
In article 4D2D9C57.2070408@knaff.lu, Alain Knaff wrote:
There normally isn't a sector 0, it usually starts at 1.
Sorry, my mistake, it's sector 1 they lack. I'm seeing numbers from 2 to F but no 1. ddrescue was seeing a single sector it couldn't read at the start of cylinders 1 to 21.
I've read/written mixed sector disks in the past, but they normally have a few huge sectors, a few smaller, and then some packing ones. Dropping from 15 to 14 seems odd, but I need to get poking around again and make note of the sizes that are reported for the sectors.
I then have no idea what happens after sector 21. ddrescue claimes to have read all the data without problems, but I'm dubious. I also expect more than 80 tracks on these disks.
I guess I'm going to have to write some fancy bash/python scripts to drive fdrawcmd to pull this stuff off (and the disks are old so I'll need lots of retries) and then some more to format and write some new disks.
Ian
+-----------------------------------------------------------+ | David C Niemi (Reston, VA, USA) niemi at tuxers dot net | +-----------------------------------------------------------+