Tape dumping, bad blocks.

From: Raymond Moyers <rmoyers_at_nop.org>
Date: Fri May 3 01:01:59 2002

On Friday 03 May 2002 00:08, you wrote:

> You might be able to even isolate the bad bits in the bad byte, or take a
> vote and use the most reported value to store into the good sector or some
> other analysis. At the very least, I would record as much of the bad
> sector as I could and write out (in a separate file) the known bad spots
> from the disk being read.

 You might be able to do some of that with a readtrack ,, hard to say
 depends on the controller i guess

 The start of a sector is all FF's or rather, stream of 1 bits then FE
 (or some other address mark) the controller then knows where it
 is in the bytestream.

 The problem with lost bits in a sector, is that all after that the controller
 no longer knows what position its in .. is the next bit the high bit of the
 next byte or the last bit of a current byte ? .. theres no way to tell
 is there ? same with a tape, well modern scsi tapes anyway, they
 are written in 512 byte blocks and here too, same thing.

 So in the floppy case or the hard disk case or the tape case,
 the next stream of 1's comes along, then the address mark
 and the controler knows where it is again and can read more
 stuff, but all after the error in the last block, floppy/disk/tape
 ya get nothing but a short read.

 Funny, on the 9 track tape you dont confront this issue.
 9 track tape is 8 bits + parity right ? so here a bad bit dont
 cause you to lose the ability to get the next byte and know
 that its a valid byte, a physical superiority it has over the
 serial streamers ?.

 Or am i assuming too much again.

 Raymond
Received on Fri May 03 2002 - 01:01:59 BST