6 Oct
2005
6 Oct
'05
6:57 a.m.
Punched the send by error.... continued.
Subject: RE: 8" floppy system needed to recover old game data
From: Allison <ajp166 at bellatlantic.net>
Date: Thu, 06 Oct 2005 09:30:01 -0400
To: cctalk at classiccmp.org
FYI: the M2FM (intel MDS) used conventional 8" drives but the FDC was really
a custom board designed by intel to do double density when there were no chips
that did it. The format must and can only be read on intel.
Subject: RE: 8" floppy system needed to recover old game data
From: "Kieron Wilkinson" <Kieron.Wilkinson at paretopartners.com>
Date: Thu, 06 Oct 2005 13:59:35 +0100
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>
My reasons for suggesting doing a track dump is so we can leave figuring
out the filesystem later... Which from my experience of other systems
means it is less likely we would get it wrong "on the day". It is bad
enough getting this done once, twice would not be too fun either. ;)
But of course, CP/M is not exactly part of my previous experiences.
CP/M file system is fairly easy to understand. It was fairly standardized
depite media variations. A dump of any form would be reconstructable
if there are no lost sectors.
For 8" systems they fell onto two major groups:
Hard sector: Altair and a Zilog used those. However _most_
hard sector 8" systems rarely carried CP/M.
Soft sector: Most common and there was a standard interchange format
for CP/M. That was 8" single sided single density (8"SSSD).
Other formats that existed were CP/M on Intel (M2FM) and
Odd sector sizes or double density. Likely formats in
the 8" realm were fortunatly fairly few (likely one of 5).
The two most common after SSSD was SSDD (single side
Double density) and DSDD (double sided double density).
The latter two SSDD was often seen and had a fairly similar
layout compared to SSSD. The DSDD was far less common and
there were a few different ideas how data should be laid down.
The 5.25 worlds was chaotic as drive were developing
and people needed to
push those minifloppies from the base of only 80k to a more useable 360
or even 780k. Where the base 8"SSSD was 256k from day one.
Even then many of the 5.25 based systems were not locked one format and
could at least read a few others. Again if it was hard sector then all
bets were off (Heath, Northstar, and a few others were hard sector).
To read base 8"sssd disks there are a lot of people that have working
systems (myself included) that have zero problem doing this. It's also
possible to do it using a compaticard or even a hacked PC FDC with the
right cable to a working drive.
If the media was 8"SSSD then reading them to the file content level is best.
IF the media is unknown and and different then it really helps to know
what the origin system was as then the format is known. If all is unknown
the reading the media at the sector level will likely get it done. That
is a slower interative process that being determine sector size, read
sectors sequentially saving them on other media, decode disk layout and
reconstruct files.
Again most 8" media is real old and there were a few brands of media that
aged poorly [worse if mishandled] with media shedding being a really big
problem.
Allison