Question about Intel disk formats

From: Richard Erlacher <>
Date: Fri Jun 22 09:20:33 2001

If it is CP/M standard format, it should be IBM3740 formatted single-density.

There are lots of other formats that work under CP/M though. I've never seen a
format with an identifying signature that was recognizable on another system.
However, since different systems have different controllers, they use different
approaches to using that controller. Interleaving rates are a common
inconsistency between systems, but 4 is a common interleave for double-density
with a 4 MHz Z80. You can get some insight into the way data layout is
implemented if you look at the directory track (track 2). If there's a
recognizable file name, then you can rigorously search for the data that
comprises that file by searching the entire diskette. If you don't have the
interleave, it doesn't matter, since directory entries are in 128-byte sectors,
derived from the Single Density format. All you need is the name of a widely
known standard file, e.g. PIP.COM. You then find the file contents, bit by bit,
and keep records of where you found each 128-byte block of the file, and then
divine the sector layout from that. It's not fun, but you only have to do it

Good luck!


----- Original Message -----
From: "Edwin P. Groot" <>
To: <>
Sent: Thursday, June 21, 2001 6:55 PM
Subject: Re: Question about Intel disk formats

> If it is CP/M format, the first track should be SD, whether or not the
> disk is formatted DD. That's how it is in the CP/M systems I have. I
> figure you should at least be able to read the first track and hopefully
> there would be a signature of what machine it's from. What I would not
> know is what interleave factor to use for the sector ordering; it seems to
> vary from machine to machine. Start with the original IBM SSSD structure.
> Edwin
> At 08:31 PM 6/20/2001 -0700, you wrote:
> >
> >
> >The disks I am trying to access are supposedly CP/M, but the labelling
> >indicates they were perhaps used on an Intel development system (they have
> >filenames on the label with ".HEX" file types; this may not mean
> >anything). If this is the case, and they were formatted on an Intel MDS
> >(and therefore M2FM), and since they are double-density, then I may not be
> >able to read them with the machines I have.
> >
> >However, I want to check their format on some CP/M machine and see if
> >perhaps I can read them. If so, then they are probably more standard DD
> >formatted diskettes, maybe even CP/M since that is what I was told they
> >are.
> >
> >Suggestions appreciated.
> >
> >Sellam Ismail Vintage Computer
> Festival
> >---------------------------------------------------------------------------
> ---
> >International Man of Intrigue and Danger
> >
> >
Received on Fri Jun 22 2001 - 09:20:33 BST

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