[Colchester] CP/M

[Wayland Sothcott]

Toby Whaymand wrote:
> Hi Wayland
>
> I don't know if you know this but the guy who sold MS-DOS to Microsoft
> ended up in court back in the early 1980's in which he admitted to "Low
> level copying" of the CP/M  code which is owned by Digital...
>
> In the book Accidental Empires by Robert Craingely that was published
> back in 1990 he argues that if Digital were not so slack, not so laid
> back they could of been were Microsoft is today!
>
>   
>
>
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>   
Toby,

I know CP/M and MS DOS were very similar. In fact the Zilog Z80 which 
CP/M ran on was a derivative/copy of the Intel 8080. The Z80 chip by 
comparison was very powerful but Intel then did the 8086 with it's 
segmented addressing allowed you to address 1Meg of ram rather than 64k 
of the Z80. I think this also played a big part in the success of MS 
DOS. The Z80 still has the best Interrupt structure, the device places 
it's number on the data bus when it hits the IRQ line, providing up to 
255 Interrupt channels. The 8086 only had 8, cascaded into 15, this is 
still a limitation to this day! Meanwhile Motorola had the 6809 and the 
68000 with innovative relative addressing meaning the operating system 
did not have to relink code depending on the location in memory the 
program was loaded to. Sinclair, Apple and Comadore were big users of 
the 68000.  Apple switched to the Power PC but strangely switch to Intel 
when the X-Box 360 switch to the Power PC. Acorn of BBC Micro fame, 
developed the Acorn RISC Machine spawning ARM (Advanced Risc Machines), 
this is the chip found in almost every PDA today. Linux runs on all of 
these but Windows is stuck on the x86 family with a special version  
available for the ARM, but that's really just Windows in name, not the 
same OS. I like the fact that you can get Debian for the Broadcom RISC 
(Reduced Instruction Set Cpu) as used in the Cobalt Qube 2 and the Links 
WRT54G and the Buffalo WHR54GS. It means you can turn virtually anything 
into a Linux server.

I used to write code in 'C' for the Z80 for embedded systems. With only 
56k of ROM the code had to be very efficient. An operating system would 
have been nice, then I could read and write disks and I would not have 
had to write my own network stack. However in many ways having an OS is 
cheating and opens up insecurities. Code burned into a chip that cannot 
be altered and can only run the one program is far more secure than 
having an operating system that can be asked to run a different program. 
Many of the devices with a CPU today run an operating system, Linux or 
VX Works or other embedded OS, this is a great opportunity to Linux fans 
to change the way these devices work.

Wayland.


Wayland.