• Please review our updated Terms and Rules here

Why didn't CP/M use a standard disk format?

Kaypro shipped a copy of Uniform with the Kaypro II in August 1982, a year after the introduction of the IBM PC. Kaypro released a free software package to convert between disk formats in 1984. The speed with which CP/M manufacturers went from proprietary formats locking in customers to needing the ability to exchange data or never sell again was astonishing.
 
NEC on their PC98 series put MS to shame regarding disk standardization. From 8" down to 3.5", all DOS disks have the same format (8x1024 byte sectors per track).
 
@Eudimorphodon, I loved your list of non-totally-MSDOS-compatibles :)

I'd add the Olivetti M20 as well as most of the "8/16" <> "816" models with dual boot.
I also discovered the "Olympia People" recently. I think all of them ran a cusomized version of MSDOS v2.x.
There's been an interesting article about the Microsoft plans for the future where this condition was clearly described as well as the plans for dealing with the console differences moving them in the BIOS.
 
For the 5.25" world there was a sort-of defacto standard. I believe the Cromemco 5.25 SSSD (18 x 128 byte sectors per track) was native readable on a number of systems including Xerox, Osborne, and Kaypro as well as TRS-80 Model 4 MM CP/M...these from personal experience. There may have been others and some vendors distributed software in that format.
 
Interestingly, neither the 8" SSSD nor the Cromemco 5.25" SSSD is readable on a stock 5150 PC. (FM encoding) It's not that it was impossible, but rather that IBM didn't consider FM to be relevant and so left support circuitry out of their design.
 
Chuck(G) said:
Interestingly, neither the 8" SSSD nor the Cromemco 5.25" SSSD is readable on a stock 5150 PC. (FM encoding) It's not that it was impossible, but rather that IBM didn't consider FM to be relevant and so left support circuitry out of their design.
Click to expand...
Somewhere I had a diagram and write up for adding FM support to the original 5150 FDC board. If I remember correctly, it didn't even involve adding more parts. Trace cuts and jumper wires to get the signal to where it needs to be.

But of course, the lack of FM support from the factory original board meant a cottage industry for companies like Compaticard.
 
The IBM preliminary design sketches for the PC included the possibility of 8" external drives and support for FM and MFM and Apple II formats in 35, 40, or 77 tracks. There was a lot of simplification to the design in order to meet the very tight delivery schedule.
 
I believe I included directions WAY back in the day how to implement FM read capability in the 5160 floppy controller (the one without the hybrid circuits that uses the WD9216 data separator) that basically involves cutting a trace and running a wire to the 765. This was likely before 1990; probably 1987.
 
Chuck(G) said:
I believe I included directions WAY back in the day how to implement FM read capability in the 5160 floppy controller (the one without the hybrid circuits that uses the WD9216 data separator) that basically involves cutting a trace and running a wire to the 765. This was likely before 1990; probably 1987.
Click to expand...
That sounds about right and may be what I was thinking about. Remember when I acknowledged your contribution to my knowledge? I think there are many points in time when that happened.

Interestingly I recently acquired a 5160 and may be able to actually implement your mod. :)
 
Then there was the Gemini Z80 with MFB (multi-format-bios) which is what Derek Fordred (CPMUGUK Librarian) used to create disks for members various machines.
He'd simply ask you to send a formatted disk with one long text file on it. Once the format was saved for MFB Derek could issue any CPMUGUK disks in an format using his Gemini.
 
No, the regular CP/M formats are usually non-specific when it comes to address marks. That's not to say that there were a lot CP/M systems with non-standard encoding, which is a completely different thing.
The problem, as I recall, wasn't that later systems didn't read sectors with the oddball address marks, but that they could not differentiate the special marks from the regular ones.
 
Chuck(G) said:
The problem, as I recall, wasn't that later systems didn't read sectors with the oddball address marks, but that they could not differentiate the special marks from the regular ones.
Click to expand...

Per the FAQ the 1791 used in the Model III fell into that category (IE, it could read the disks but not tell the difference, which was at least good enough to allow the data to be consumed), but it names at least one common PC disk controller chip that can’t make sense of them at all?

I remember that none of the disk controllers I had in the PCs I owned in the late 90’s could make any sense at all of Model I disks, but I think the barrier there was double density, period.
 
You must log in or register to reply here.
Back
Top