27 Aug
2005
27 Aug
'05
3:57 p.m.
Subject: Re: Bit of CP/M trivia needed
From: Steve Thatcher <melamy at earthlink.net>
Date: Sat, 27 Aug 2005 18:13:27 -0400
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>
what machine and/or controller was this that had no ROM at all? I
never have dealt with any system that at least didn't have some type
of startup code somewhere other than a disk drive. DMA would need to
be setup unless it was hardwired. The original Intel Intellec-8
required that you enter a program jump into memory that pointed to
the program monitor. Intel didn't call it a BIOS though.
>Hi
> 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.
>Dwight
There were a few later machines that used shadow boot rom
(it was a doide matrix) and one I know of that the hardware
dma was programmed to grab the first sector at reset but
the dma logic dwarfed the CPU. There was a slightly later
machine that could also do that but, the real trick was the
FDC was a second cpu with rom and it know that if it saw
reset it was to find the boot block and copy it to ram
@0000h so the main cpu ran on release from DMA hold and reset.
However early machines were ot so extravagant with hardware
as it was mostly SSI TTL and to do dma it nearly doubled
the total system package count (without counting ram). An
8080 system needed a lot of support components.
In the end it's irrelevent to the basic question asked.
The CPM system from at least V1.3 on generally depended
on some kind of program (however small) to boot the first
block or blocks the usual mode was to load the CP/M image
as a monolithic chunk of code and then execute it. In most
cases the amountof code needed to do that would fit in the
then available 256byte EProms/fuse roms ( either 1702 or bipolar).
Allison