MP/M 815, CCDOS of its variations and HDD formats ?

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Gary S

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Mar 14, 2022, 12:41:53 AMMar 14
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My memory is failing me a bit as I never really got too involved in the later stages of the various DR operating systems after they were sold on.
So my question is how backward compatible where they ?
I am thinking what were the issues of a cp/m80 programs accessing the hard/floppy disk, the various formats, layouts etc.

Gary
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Peter Higgins

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Mar 15, 2022, 4:51:20 PMMar 15
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Presumably you are referring to the "8-16" versions of Digital Research CP/M, MP/M, and Concurrent CP/M or Concurrent DOS. These "8-16" versions were not developed directly by DR - they were customized versions developed by a couple of computer manufacturers for use on their own hardware systems, most notably CompuPro. All CP/M-80 BIOS calls were managed by the customized 8-16 operating system (including those accessing the floppy and hard drives) therefore either CPM/80 or CPM/86 applications could both be handled seamlessly. The method of implementation changed as the operating systems evolved, using the BIOS and a customized CCP in early versions, and a shell environment created by a "SWITCH" application in later versions. Backwards compatibility was excellent, provided the CP/M-80 application did not attempt to directly access hardware.

Gary S

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Mar 15, 2022, 5:54:20 PMMar 15
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Thanks Peter,
Answered the basic for me, I just wondered how they managed the compatibility of hard disk formats etc between the different for os's.

such as max 8mb for cpm80 compared to msdos limits.

Presumably in the "switch" application it seems...

Douglas Miller

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Mar 15, 2022, 6:14:17 PMMar 15
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The hard disk formats you seem to refer to are filesystem, not track/sector, formats. Programs that made BDOS calls to access files did not need any special compatibility layer, unless they hard-coded redundant checks for the limits (e.g. instead of just letting the BDOS tell you when you exceed the file size limit they pre-emptively checked for that limit).

Douglas Miller

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Mar 15, 2022, 7:08:21 PMMar 15
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On Tuesday, March 15, 2022 at 5:14:17 PM UTC-5, Douglas Miller wrote:
> The hard disk formats you seem to refer to are filesystem, not track/sector, formats. Programs that made BDOS calls to access files did not need any special compatibility layer, unless they hard-coded redundant checks for the limits (e.g. instead of just letting the BDOS tell you when you exceed the file size limit they pre-emptively checked for that limit).

Well, except for possible differences between 16-bit and 8-bit FCBs, and the like.

Peter Higgins

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Mar 15, 2022, 8:24:36 PMMar 15
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Most of CompuPro's 8-16 systems used the CPM/86 and Concurrent CP/M86 file systems on both floppy disks and hard drives.
Only the final versions of CompuPro's Concurrent CP/M86 and Concurrent DOS used the MSDOS FAT file system.
The "SWITCH" application provided with the later 8-16 operating systems just needed to set up a virtual CP/M-80 environment, translating BDOS calls between it and the 8-16 operating system.
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