Minimal CP-M SBC design - test-drb@ccmp.vtda.org

11 May 2008

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Subject: Re: Minimal CP-M SBC design
   From: Dave McGuire <mcguire at neurotica.com>
   Date: Sun, 11 May 2008 08:23:13 -0400
     To: General Discussion: On-Topic Posts Only <cctech at classiccmp.org>

Chuck Guzis wrote:
      I
dunno Chuck...the only reason more CP/M systems weren't ROM- 
 resident back in the day was due to convention, not technical  
 restrictions.  I (personally) don't think there's anything  
 non-"period" about ROM-ing CP/M.  
 It's not the ROM-ing of CP/M that disturbs me, but rather the 
 "disklessness" of the thing.  Wasn't the whole idea of CP/M 
 originally to give you something to manage files on your floppy 
 drives?  I mean, that's what the bulk of the code in CP/M is for--
 heaven knows, the support for other I/O is nothing to write home 
 about. 

 If one wants to enjoy a "vintage" experience, what sense is there in 
 being diskless?  At any rate, even something as simple as a WD1770-
 type controller added to the design would give that capability with a 
 minimum of support "glue".  

 Alternatively, one could stay diskless and add a sound-effects module 
 to emulate the "chunk" and "grrr" of a head-load and seek--and the 
 "thunk-click" of a drive door being opened and a floppy inserted.   
   Well I wasn't talking about a diskless system...only one in which 
CP/M itself was in ROM. 
When I mentioned it I wasn't running CP/M from rom which by the way
takes recoding of the CCP, BDOS and BIOS to make all the data areas
external.  What I was refering to is simply booting it from a rom rather 
than off the system tracks.  The result of that is then ANY formatted disk
is a boot media and makes the system a bit more bullet proof as a 
common fault (STILL) is trying to boot a nonsystem disk or worse having
a power glitch kill the system tracks.

When done that way CP/M is still in ram, can be overlayed, and even 
patched.  Boot from rom also solves the chicken/egg paradox as the
the system disk does not have to have data/programs.

...
   I still
don't have the hang of this "vintage" thing yet, probably 
 because I'm vintage myself.  Please forgive my density... 
   I often suffer from the same problem.  I think very few of us, even 
here, actually used stuff like CP/M and PDP-11s when they were 
considered current technology. 
Speak for yourself.  I wish that were true.  The first version of CP/M
I ran was 1.3 When it was available and 1.4 was much better and useful.
I had access to PDP-8 ion 1969 and PDP10 in 1971 and got my first PDP11
in 1980(still have it too!). PDP11 stopped being current in the 1990s 
when DEC sold the tech and licenses. Up till then you could buy it new 
and faster (and then from mentec for years after that).

Allison

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         -Dave

-- 
Dave McGuire
Port Charlotte, FL 