IBM 610 workstation computer 3457

Andrew Swallow

Its interesting how things change over time. If you read the early history of computers, the ability to have software modify itself was considered a very important feature. Much later on, in the early days of microprocessors, it was also helpful in overcoming certain weaknesses in the processor's instruction set. I used it a number of times to implement fast indexing schemes as well as calculated branch tables to good effect. But as you say, current architecture pretty much eliminates any such need. Even back then it was a pain if you wanted to put something on ROM or expand the capabilities of limited memory by loading different images in the same area of memory for partial end. For ROM, the easy way around was to just use the ROM to load RAM at start up. As to "overlays", we would fragment the code such that the areas with intermediate results would remain in memory all the time but the rest of the code could be overwritten then brought back in at a later time with the old index or branch tables still intact. Ah the good olde daze (NOT!)

Chris AN GETTO$;DUMP;RUN,ALGOL,TAPE $$