Bit of CP/M trivia needed

Dwight K. Elvey dwight.elvey at
Tue Aug 30 12:14:15 CDT 2005

>From: "Joe R." <rigdonj at>
>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

 Yes, what I meant to say was for the S-100. I was told that the first
S-100 implementation used this type of board. I knew Gary used a

><>. 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.
>   Joe
>   Joe

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