The Importance of Terminology's Quality

Martin Gregorie martin at see.sig.for.address.invalid
Sun Aug 24 14:28:01 CEST 2008

On Sat, 23 Aug 2008 21:22:05 -0400, John W Kennedy wrote:

> Martin Gregorie wrote:
>> On Sat, 23 Aug 2008 00:06:28 -0400, John W Kennedy wrote:
>>> Martin Gregorie wrote:
>>>> Not necessarily. An awful lot of CPU cycles were used before
>>>> microcode was introduced. Mainframes and minis designed before about
>>>> 1970 didn't use or need it
>>> No, most S/360s used microcode.
>> I never used an S/360.
>> I thought microcode came into the IBM world with S/370 and Future
>> Series (which later reappeared as the AS/400, which I did use). Didn't
>> the S/370 load its microcode off an 8 inch floppy?
> Some did, but not all. The 370/145 was the first, and made a big splash
> thereby.

Thanks for that. As I said, during most of that era I was using ICL kit. 
Microcode was never mentioned in the 1900 contect. Hoiwever, they had a 
very rough approximation called extracodes. though they were closer to 
software traps than microcode: if hardware didn't implement an op code 
the OS intercepted it and ran equivalent code. This was used for i/o 
operations and for FP instructions on boxes that didn't have FP hardware.
As a result all boxes executed the same instruction set. Some opcodes 
might be very slow on some hardware but it would execute.

The 2900 series had huge amounts of microcode - it even defined both 
memory mapping and opcodes. You could run 1900 code (24 bit words, fixed 
length instructions, ISO character codes) simultaneously with 'native' 
code (8 bit bytes, v/l instructions, EBCDIC) with each program running 
under its usual OS (George 3 for 1900, VME/B for 1900). 

The only other systems I'm aware of that could do this were the big 
Burroughs boxes (6700 ?), which used a byte-based VM for COBOL and a word-
based VM for FORTRAN and Algol 60) and IBM AS/400 (OS/400 could run S/34 
code alongside S/38 and AS/400 code). AFAICT Intel virtualisation doesn't 
do this - all code running under VMware or any of the other VMs is still 
running in a standard Intel environment.

martin@   | Martin Gregorie
gregorie. | Essex, UK
org       |

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