On Mon, Dec 05, 2016 at 12:05:39PM -0500, Paul Koning wrote: > > > On Dec 4, 2016, at 10:12 PM, Bob Supnik <[email protected]> wrote: > > > > Josh Dersch at the Living Computer Museum found a snippet of real DECtape > > code (that runs on a real 11/40) which fails on the simulator. > > ... > > This leads me to think that there's a second principle to bear in mind when > > simulating older machines. The first is "economy of gates". In early > > systems, gates were precious, and the hardware tended to implement no more > > than the minimum functionality required. Error checks were a luxury and > > were often omitted. > > This makes me wonder about the fuzzy line between quirky features and > sort-of-bugs. The code snippet you mentioned sounds like it falls on the > side of the "quirky", and it sounds right for the simulator to implement > that. On the other hand, there's one I recently read about a machine in > which a subroutine call instruction would fail with the stack pointer equal > to -0, but when the stack pointer was +0 it would produce an address error > only for some of the addressing modes. "The schematics ... confirm this; the > reason is unknown" says the article. Implementing that sort of corner case > is obviously doable, but not necessarily all that useful. >
Are you suggesting that simulators should fix "bugs" for someone using a simulator for comparison when restoring real hardware it could be very confusing. (not that such comparisons should be truated anyway) /P _______________________________________________ Simh mailing list [email protected] http://mailman.trailing-edge.com/mailman/listinfo/simh
