Date   : Tue, 07 Apr 2009 10:32:11 +0100
From   : profpep@... (Mike)
Subject: Writing BBC Disc Images on Linux

I used to do a lot of word processor file exchange stuff, back in the day
whentehre were few standards.

Writing 40 track floppies on an 80track drive if a bit fraught. The proble
is imple. The head is literally half as wide on the 80 track. If you were
writing a virgin dic, then you end up with a 40 track dic with narrow
tracks. This isn't bad, and in fact I've never had one fail to read.in the
target drive. If writing to a used disc, the data will be over written,
leaving a stripe of old data present. I'm not so au fait with the read write
heads on floppies, to know if they erase before write, (hard discs used to
have 'tunnel erase', which left a blank strip down each side of newly
written data, but I can't keep up with the way they work nowadays, and low
level acces to modern hard discs is difficult).

If, as most people will be doing nowadays, you are over-writing an old disc,
well there might be problems. Depending upon the actual alignment of the
target drive, it may get a mix of old and new data, leading to sector errors
etc. I discovered this back in the days of BBC's in schools, when some
schools had a mix of 40 and 80 track drives, and some drives were
switchable. The rule was: "If writing a 40 track disc in an 80 track drive -
Use a new disc". I have meant to experiment with putting some old floppies
through a bulk eraser, to see if all traces of the original format can be
removed. It would be useful if they could be.

||\/||ike