Any own an 11/725...?

[CRC]

On Mon, 24 Oct 2005 05:00:57 +0100 (BST), ard at p850ug1.demon.co.uk  
(Tony Duell) wrote:

>
>>> The 11/730, of course, is mostly PALs (as I said) with some RAM as a
>>> control store, 8 off 2901s as the ALU, and an 8085 (I think) to  
>>> load the
>>> control store, etc. One day I am going to look into modifying the
>>> microcode of that machine...
>>>
>>
>> To what end?  Increased performance?
>>
>
> NO, just for fun... I doubt very much I could improve on the  
> performance
> for running the VAX instruction set. I have not looked at the prints
> carefully enough to determine how much of the instruction set is
> hard-wired (if any), I wonder if it would be possible to run a  
> different
> instruction set entirely.
>
> -tony
>
>

Actually, with access to the micro instructions you can often  
substantially improve the run-time of a given program. The Modcomp II  
had the microbus accessible for use along with a number of unused  
instructions. The communications instructions and floating point were  
implemented using this bus.

I implemented an instruction store attached to this bus and which  
allowed me to create and store new instructions. A friend working on  
a CS Phd in pattern matching ginned up a program that would find  
common instruction sequences in a program, deconstruct the microcode,  
perform optimization on the sequence and then create a new  
instruction which was substituted for the original sequence. We often  
got increases of performance of 20% over the original code.

IIRC the Burroughs computers would load a different instruction set  
depending on what language was being used. Tony could create a VAX  
with Forth as the instruction set ;-)

     CRC