25 May
2021
25 May
'21
1:12 p.m.
On Tue, 25 May 2021, Peter Coghlan via cctalk wrote:
Early on, floppy disks on the BBC Micro were 5.25in FM
with 10 sectors
per track and 256 bytes per sector. However, BBC Micros are probably not
common where you are and some programming in 6502 assembly or BBC Basic
and a knowledge of the Osbourne filesystem would be required.
I might be persuaded to offer the use of a BBC Micro and to do the
programming if it is feasable to send me the disks and details of the
filesystem involved, assuming a more convenient solution doesn't come
up.
That should be very suitable for the FM SIngle Density ones, as that is
the same physical format.
Osborne was an ordinary CP/M, which is fairly well documented. I don't
have convenient access right now to the parameters.
Basically, there is a boot sector and system track(s) (How many
"reserved"/system tracks varies).
Then there are sectors with the directory (how many sectors varies)
In the Directory, each file entry is 32 bytes, with the file name and a
list of blocks that the file occupies on the disk.
If there are more blocks than will fit in the list in the directory entry,
there is a second entry for the file.
Each block is 8 or 16 128 byte records (which are often called "sectors"
to confuse you.
On old versions of CP/M, if the machine is available, STAT DSK: will tell
you most of the parameters. What it doesn't tell you is the physical
sector size (how many LOGICAL "sectors" are in each physical sector),
interleave, and, on double sided disks, whether the second side acts as
continuation of the first side tracks, or whether the second side tracks
come after the first side tracks starting at the inner OR outer tracks.
And, there can be numerous other oddities, . . .