Path: utzoo!attcan!uunet!mcvax!hp4nl!phigate!philmds!leo From: leo@philmds.UUCP (Leo de Wit) Newsgroups: comp.sys.atari.st Subject: Re: Multitasking on the ST Message-ID: <1071@philmds.UUCP> Date: 12 Aug 89 16:39:09 GMT References: <8908021826.AA05333@ucbvax.Berkeley.EDU> <15627@watdragon.waterloo.edu> <652@opal.tubopal.UUCP> <471@tw-rnd.SanDiego.NCR.COM> <1066@philmds.UUCP> <482@tw-rnd.SanDiego.NCR.COM> Reply-To: leo@philmds.UUCP (Leo de Wit) Organization: Philips I&E DTS Eindhoven Lines: 53 In article <482@tw-rnd.SanDiego.NCR.COM> johnl@tw-rnd.SanDiego.NCR.COM () writes: |In article <1066@philmds.UUCP> leo@philmds.UUCP (Leo de Wit) writes: [] |>I think two issues are being confused here, the need for per process |>memory protection, and the possible to run processes 'simultaneously'. |>Why should memory protection be a hotter item when parallel processes |>are involved? | |Because of the potential for a single user program to cause the termination |of all the processes in the system. This is equally well possible in the current 'one-process-running-at-a-time' scheme. Note that there are already accessory-based editors, batch modem transfer programs, TSR print spoolers for the ST right now. |Consider: You are a user of the Spiffy multi-tasking-but-no- |per-process-memory-protection Machine. You fire up a ray-trace. [etc. good example left out] | |On a machine with memory protection (OK and resource tracking) the MMU will |prevent corruption of other processes address space, and the nasty process can |be removed from the system cleanly. I think you'll need a bit more than just an MMU for a secure system. S'pose your nasty process alters some system vector (applying patch 271 to SAFEDOS). A pity that the last bug was not yet removed... My point is, that a MMU is a probably undispensable ingredient IN AN OTHERWISE EXCELLENT SYSTEM. That safe system (which undoubtedly will have a notion of privileges, users) is what you should start with in the first place. B.T.W. what do you do when a thunderstorm is coming up, but your raytracer has yet to finish its last hour of calculations? Use a TMU :-) ? [] |I'm all for system robustness for ANY system. My point is that when you |introduce multitasking, memory protection is more important due to the |potential to disrupt other processes. I heard this one before and I still won't believe it, unless a proper argument is given. |>[about VM] | |Sounds Good! But now you're wandering into the area of virtual memory and |that's not what our original discussion was about. Thanks for the reply. You bought an MMU but you don't want VM? Gee, that would be the first reason I would buy an MMU for (and not for protection). As long as the filesystems used are single-user, not write protectable, I don't care much for safe core. Leo.