Re: Extracting files off “unknown” 8 inch disks. Any thoughts…

dwight dkelvey at
Mon Apr 17 09:34:03 CDT 2017

Hi Tez

 You where lucky. You had a format that was more or less standard. I have disk done in formats that are not so common.

One was a real toughie. I had some 5.25 and some 8 inch hard sectored disk in MFM format. These were for the Polymorphic machines. I'd modified a Polymorphic 8 inch controller to run at the lower frequency of the 5.25 disk and was able to read most all of the 5.25 disk. This was the bulk of what needed to be done. I used my Poly88 as the reader and controlled it remotely from my PC through the serial lead.

I'd never got the time to reconfigure the controller board for the 8 inch disk. I finally got help form Chuck who was able to extract the data. Ihad to parse it into files but that was the easier part.

These are not in the common Polymorphic format that used the controller similar to the NorthStar. These were still hard sectored but MFM instead of FM. It was non-standard because it didn't use the ID and other MFM soft sectored markers.

What was cool about the 8 inch disk is that they contained the entire source code for the BASIC that Polymorphic used.

As an example of other formats, my Nicolet 1080 uses 8 inch 32 hard sectored disk and formats them as only two sector per track of 512 20 bit words.

None of these formats would read correctly on a PC controller.

One of the bit timing formats type of reader would have been needed.


From: cctalk <cctalk-bounces at> on behalf of Terry Stewart via cctalk <cctalk at>
Sent: Monday, April 17, 2017 3:19:33 AM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Extracting files off “unknown” 8 inch disks. Any thoughts…


Just an update on this.  I still haven't got those 8' floppies of unknown
origin to play with but I HAVE made a lot of progress with my own disks.
Thanks to everyone who gave me help with this.

Here's a writeup for those interested:
Adventures with an 8 inch (8”) disk drive - Part 1. New acquisition: A Mitsubishi M2896-63<>
This page contains part 1 of an article on disk imaging experiences with an 8 inch disk drive

Terry (Tez)

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