Re: Questions on Disk ][ error checking

[sicklittlemonkey <nick.westgate@gmail.com>]

On Nov 12, 6:15 am, dog_...@macgui.com (D Finnigan) wrote:
> As I understand it, checksums are used to verify that the data read from the
> disk are valid and error-free.
...
> Also, would there ever be a circumstance where the disk has become damaged
> in an area such that the Disk ][ cannot tell whether a bit is 1 or 0 and
> thus refuses to read that disk?

Just FYI, I once saw these facts combine in interesting way. There was
an error on a particular sector, and with a sector editor that ignores
errors (perhaps the CIA Files) I could read that sector and the data
would change with every read.

There was obviously a bit flip or slip, and the error propagated into
the following data. In this case I could just read the sector until I
saw good data and then wrote it back to disk. No problems after that.

Of course, this kind of manual correction is only practical if (1)
there aren't too many errors, and (2) you can easily tell if the
sector data is good or bad.

Cheers,
Nick.