One interesting thing about CP/M is that it didn't have subdirectories.
"CP/M 2.2 had no subdirectories in the file structure, but provided 16 numbered user areas to organize files on a disk. To change user one had to simply type "User X" at the command prompt, X being the user number."
MS-DOS (and PC-DOS) also didn’t have subdirectories until version 2.0.
These were floppy disk oriented operating systems, and at 360 kB per floppy, directories were not really that useful.
Hard disk support made it more urgent to offer Unix-style directories. Since the forward slash was already used for CLI parameters in the CP/M style, it couldn’t be used as the path separator. So Microsoft chose the backslash instead, and it persists in Windows today.
> Since the forward slash was already used for CLI parameters in the CP/M style, it couldn’t be used as the path separator. So Microsoft chose the backslash instead, and it persists in Windows today.
And arguably more file loaders than operating systems as such. I long thought it a sort of interesting question how things could have turned out differently if one of the many 16-bit operating systems (or Unix of course) kicking around in the minicomputer world had been more widely used on early PCs.
Some of the products mention on that piece were true operating systems.
MP/M and its derivatives (MP/M-86, CCPM, CDOS) were all multitasking, multi-threading, multi-user, multi-terminal/console real time preemptive OSs. The bank switching versions also had a form of memory protection.
CDOS-68k, CDOS-286 and the subsequent renamed to FlexOS products also had those capabilities, but with inherent memory protection.
So it is only really the basic CP/M-86 product (lacking the MP/M bits) which was the simple program loader.
In many ways the FlexOS product are sort of inspired from the DEC minicomputer RSX-11m OS; and the MP/M derivatives look like they were inspired by DEC RSX-11d (and hence RSX-15).
I was an MP/M 2 user (Altos) for a while. It was a great system for a small workgroup, supporting a handful of (Volker Craig) Terminals. VT-52 clones IIRC.
Fair enough. I suppose that hardware resource constraints were sufficiently tight at the time that the "mass market" wouldn't have thanked you for something that might have cost twice as much (at a time when micros were already quite expensive relative to today).
> And arguably more file loaders than operating systems as such
That's a bit unfair. They also provided file operations and hardware abstraction. That way, it didn't matter how your disk IO was implemented (CP/M on Apple II's used the 6502 for that) and your code could be exactly the same.
IIRC, Unisys's MCP doesn't have directories, just very long file names with separators in them. It's up to the applications to present that as a hierarchical namespace.
Now that I mention it, it'd be interesting to play with Apple's DOS 3.3 (33 char file names) that way.
"CP/M 2.2 had no subdirectories in the file structure, but provided 16 numbered user areas to organize files on a disk. To change user one had to simply type "User X" at the command prompt, X being the user number."
https://en.wikipedia.org/wiki/CP/M