Bit of CP/M trivia needed

Joe R. rigdonj at
Tue Aug 30 10:23:43 CDT 2005

At 02:40 PM 8/27/05 -0700, Dwight wrote:
>>From: "Allison" <ajp166 at>
>>>Subject: Bit of CP/M trivia needed
>>>   From: "Brian Knittel" <brian at>
>>>   Date: Sat, 27 Aug 2005 00:58:01 -0700
>>>     To: cctalk at
>>>Hi all,
>>>Does anybody out there know for certain when the 
>>>term BIOS was coined? I believe it was Gary Kildall,
>>>and from what I can find, it was around 1978 that
>>>he abstracted the I/O and localized it in what
>>>he called the BIOS. Anyone know differently?
>>The term BIOS is older, early '77.  It came into use with 
>>V1.3 I think and for cetertain in V1.4.
>>>Also -- was the BIOS stored on the CP/M 
>>>floppy, or was it in ROM/EPROM? If not, how
>>>did CP/M machines boot? Was there a dedicated
>>>boot ROM that was used just for startup, and
>>>then the BIOS took over? I had one back in
>>>the day, but I sure can't remember this detail.
>>The easy answer is yes.  Tranditional CP/M systems the 
>>CCP/BDOS and BIOS were on the first two reserved tracks 
>>of the floppy (8" SSSD) and those were loaded by a boot 
> My understanding was that the first ones had no ROM
>and used a DMA controller that loaded bootstrapping
>code from the first sector on reset. I have such a
>controller on my machine. All RAM, no ROMs.

    I don't think so. CPM was first written by Gary Kidall for the Intel
MDS-800 (go read the CPM docs) and they NEVER had DMA capability. They used
a 2k bit bootstrap loaded in a 1702 EPROM. Here is a picture of a MDS-800
with THE actual 1702 Boot EPROM
<>. The 1702 is mapped
into and out of the memory space by the BOOT switch on the MDS front panel.
Allison's description is dead on. Dave Mabry is the expert of the Intel MDS
and he can provide more details about how they're booted and the BIOS table
is loaded. FWIW Gary had a contract to write PL/M for Intel and wrote CPM
as a file handling system for use in developing PL/M. He offered Intel CPM
but they didn't want it since they were working on their own OS.(BIG
Mistake!) Intel's OS was released as ISIS and was only used in the Intel
MDS systems (although I've heard they did have a PC version for a PC based
MDS). ISIS is very crude compared to CPM.

   MDS 800  <>

   You might also want to take a look at 'CP/M and a brief history lesson'
here;  <>. I used to have the exact
quotes from Gary but unfortunately the link to them is now dead.



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