mbjr@maxwell.ece.cmu.edu (Mauricio Breternitz) (07/28/89)
The (now ancient) IBM 1130 also had the three index registers at memory locations 1, 2, 3 Mauricio
jgd@csd4.milw.wisc.edu (John G Dobnick) (07/29/89)
From article <8907281547.AA28878@maxwell.ece.cmu.edu>, by mbjr@maxwell.ece.cmu.edu (Mauricio Breternitz): > The (now ancient) IBM 1130 also had the three index registers > at memory locations 1, 2, 3 The (even more ancient) IBM 1620 (model II) not only had index registers in memory (reasonable, since it was a memory-to-memory machine), but it had two software-selectable "banks" of them. "Software-selectable" meaning the program could select one bank, the other bank, or *neither* bank of index registers. One could also programatically turn indirect addressing on or off. And, of course, it used base-10 arithmetic -- none of this binary nonsense! Interesting machine. -- John G Dobnick Computing Services Division @ University of Wisconsin - Milwaukee INTERNET: jgd@csd4.milw.wisc.edu UUCP: <backbone>!uwvax!uwmcsd1!jgd "Knowing how things work is the basis for appreciation, and is thus a source of civilized delight." -- William Safire
clements@bbn.com (Bob Clements) (07/29/89)
From article <8907281547.AA28878@maxwell.ece.cmu.edu>, by mbjr@maxwell.ece.cmu.edu (Mauricio Breternitz): > The (now ancient) IBM 1130 also had the three index registers > at memory locations 1, 2, 3 The not-quite-so-ancient-as-an-1130 DEC PDP-5 had the Program Counter in core memory, at location zero. The bootstrap loader (which read programs at 110 BPS from the reader of the Model 33 TTY) used this feature to transfer to the newly loaded program. Just read a datum into location zero, and suddenly you were no longer running in the bootstrap. The PDP-8, largely compatible with the PDP-5, had its PC in flipflops. So the bootstrap had to recognize stores to zero and treat them as jumps. /Rcc Bob Clements, K1BC, clements@bbn.com