"CP/M compatible" vs. "MS-DOS Compatible" machines?

[Chuck Guzis]

> Date: Sun, 03 Feb 2008 07:34:54 -0500
> From: Allison 

> NOvados, DOS+, ZRdos, Zsdos and ZCPR addons to CP/M. 

There were also the independent implementations such as TPM (for the 
QX-10) and TuboDOS.  There were others, even a a couple that provided 
the capability to run CP/M 2.2 programs under non-CP/M OS Z80 
platforms.  CP/M, particularly 2.2 was easily cloned.  Most 
applications used the information in the reference manual set and 
didn't rely on "undocumented" features.

IIRC, the bigger problem when MP/M came along, was trying to work 
with those programs that were just plain sloppy and performed file 
open requests without closing the file (since CP/M didn't even keep 
so much as an open file count, you could be very sloppy, even opening 
a file multiple times or not at all (as long as you filled in the FCB 
fields correctly).  Some programs saved FCBs and then used them 
later.  

I wanted to add a "put that diskette back" alarm to my CP/M 
implementation when there were files opened for writing (one needn't 
even turn on the drive motor--just periodically sample the write-
protect status; a diskette being inserted or removed will toggle it a 
couple of times). I'd already done it for DX-85M and it reduced our 
diskette file corruption problems to nearly zero.  That "R/O error" 
diagnostic from CP/M was unreliable at best and nearly useless even 
when it worked.

It was then that I discovered that CP/M made no attempt to track open 
files and indeed, the behavior of many programs depended on this.

Cheers,
Chuck