[Coco] Re: Re: Re: Disk Basic and 512 byte block floppies.

[KnudsenMJ at aol.com]

In a message dated 1/22/04 8:38:50 PM Eastern Standard Time, 
hcmth019 at csun.edu writes:

> PS As you may gather I spent a fair amount of time working with CPM
>  directory details.

OK.  As I dig farther back into my rotting memory cells, I'm wondering if I'm 
not remembering a system based on a Data General Nova minicomputer (older 
than our chip-based toys, for sure).

In one of my odder job assignments, we had to reverse-engineer a competitor's 
office telephone system, given nothing but one 8" (!) floppy.  We acquired a 
drive for it, and a buddy used some hardware to read each track raw and record 
the magnetic flux changes off each track.  Then, based on a library book's 
description of MFM and other encoding techniques, I wrote a program to convert 
the flux changes into 0s and 1s and ultimately bytes and sectors.  It was 
amazingly educational, and successful!

We found lists of names and phone numbers in there, and tons of binary 
executable code.  More library research revealed that the unknown hardware was a DG 
Nova, one of the most popular industrial minis of its day.

Why I think the file system was CP/M, I don't know, maybe from the 8" floppy? 
 Or I'm merging two projects in my memory?  Anyway, the files had sectors 
linked together.  Given that the Nova was much older than CP/M, you can imagine 
that the file system design was maybe not the best.

FWIW, you probably couldn't find that book in any library today, except the 
sub-sub-basement of the Lib of Congress.  Or some dedicated collector's Web 
site.
--Mike K.