From mboxrd@z Thu Jan 1 00:00:00 1970 From: cowan at ccil.org (John Cowan) Date: Fri, 27 Nov 2020 11:22:00 -0500 Subject: [TUHS] Apple IIe Unix? In-Reply-To: <20201127115444.E581018C091@mercury.lcs.mit.edu> References: <20201127115444.E581018C091@mercury.lcs.mit.edu> Message-ID: On Fri, Nov 27, 2020 at 6:55 AM Noel Chiappa wrote: > The thing that takes special hardware is _protecting_ one task from a bug > in > another - a bug which could trash the first tasks's (or the system's!) > memory. One has to have memory management of some kind to do that. > Actually, a modified version of the * approach will also work. When switching processes, swap the whole process out to your fastest device (on * this was a single write to the drum) and swap in the new process. * hardware had a bounds register, so it was only necessary to swap out enough of the previous process to fit the smaller process in. So after a while, core started to look like an onion, with the current process at the bottom and pieces of larger non-current processes above that. (I thought that * was MIT CTSS, but I can't confirm that.) As for interrupts, the stock 2e has both IRQ and NMI lines. Erann Gat aka Ron Garret explains in < https://www.atarimagazines.com/compute/issue9/030_1_THE_25C_APPLE_II_REAL_TIME_CLOCK.php> how to make an external clock and hook it to the NMI pin for 25 cents in 1981 dollars (about $1.67 today; h/t measuringworth.com). John Cowan http://vrici.lojban.org/~cowan cowan at ccil.org A mosquito cried out in his pain, "A chemist has poisoned my brain!" The cause of his sorrow / Was para-dichloro- Diphenyltrichloroethane. (aka DDT) -------------- next part -------------- An HTML attachment was scrubbed... URL: