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. > ..snip...
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 | -- http://mail.python.org/mailman/listinfo/python-list
