Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!ncrlnk!ncr-sd!tw-rnd!johnl From: johnl@tw-rnd.SanDiego.NCR.COM (John Lindwall) Newsgroups: comp.sys.atari.st Subject: Re: Multitasking on the ST Message-ID: <482@tw-rnd.SanDiego.NCR.COM> Date: 11 Aug 89 20:16:18 GMT References: <8908021826.AA05333@ucbvax.Berkeley.EDU> <15627@watdragon.waterloo.edu> <652@opal.tubopal.UUCP> <471@tw-rnd.SanDiego.NCR.COM> <1066@philmds.UUCP> Reply-To: johnl@tw-rnd.SanDiego.NCR.COM () Organization: NCR Distributed Systems Laboratory Lines: 56 In article <1066@philmds.UUCP> leo@philmds.UUCP (Leo de Wit) writes: >In article <471@tw-rnd.SanDiego.NCR.COM> johnl@tw-rnd.SanDiego.NCR.COM (John Lindwall) writes: >|Amen to that! Amiga owners have suffered with the lack of an MMU. The >|usefulness multitasking is a given, IMO. The security of Amiga's multitasking >|is poor due to the lack of memory protection supplied by an MMU. Those of >|you who agree multitasking is useful, and would like to see it on an Atari: >|Demand it from Atari and demand MMU support as well. > >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. Consider: You are a user of the Spiffy multi-tasking-but-no- per-process-memory-protection Machine. You fire up a ray-trace. It'll finish in 12 hours so you start up a terminal program and download some cool PD software from a BBS. While thats all going on "in the background", you fire up your compiler and start writing a new program. You run your program and it has pointer error which causes random data to scribbled across memory. The machine crashes --- badly -- all of the processes on the machine terminate and the system reboots. 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. > In the current situation it is just as well feasible for >instance by an application program to thrash the space of the shell it >was invoked by. So if you insist on security, you should insist on it >right now already. > 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. >An MMU alone probably won't hack it; you will probably want a 680x0 >(x >= 1) to be able to page in new memory (a 68000 doesn't maintain >enough internal information to be able to restore correctly from a >BUSERR). > > Leo. 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. ---------------------------------------------------------------------- John Lindwall johnl@tw-rnd.SanDiego.NCR.COM "Above opinions are my own, not my employer's" Health is merely the slowest possible rate at which one can die.