swklassen@dahlia.waterloo.edu (Steven W. Klassen) (08/07/89)
In article <652@opal.tubopal.UUCP> alderaan@tubopal.UUCP (Thomas Cervera) writes: > > What's all this about MultiTasking on the ST ? You don't have a MMU (not >really and I think that's the worst failure in the ST's hardware architechture), >so you are definetely not able to run a *secure* multitasking on this machine >even if you want to - basta. All what you can call protected memory inside the >ST is a bunch of bytes at the bottom plus the hardware registers - that's it. > If you want to realize reasonable memory segmentation (in my experience this >is essential for TimeSharing) you MUST have a MMU. > >-- >Thomas Cervera | UUCP: alderaan@tubopal.UUCP >SysMan RKOpdp (RSTS/E) | alderaan%tubopal.UUCP@TUB.BITNET (saves $$$) >D-1000 Berlin 30 | ...!pyramid!unido!tub!opal!alderaan >Motzstrasze 14 | BITNET: alderaan%tub@DB0TUI11.BITNET Oh really? Then how do you explain the appearance of Minix (a Unix look-alike) for the Atari ST? I have cross posted this to the Minix newsgroup. I thought you (Thomas) might be interested in telling those who gave the ST multitasking just why what they have done is not possible. I agree that the Atari hardware is not designed for multitasking but that does not make it impossible, only less efficient. By creating multitasking systems for the ST (like Minix and MX2) people are telling Atari that we want multitasking and would like the hardware to support it. Steven W. Klassen Computer Science Major University of Waterloo
alderaan@tubopal.UUCP (Thomas Cervera) (08/08/89)
In article <15706@watdragon.waterloo.edu> swklassen@dahlia.waterloo.edu (Steven W. Klassen) writes: >In article <652@opal.tubopal.UUCP> alderaan@tubopal.UUCP (Thomas Cervera) writes: >>so you are definetely not able to run a *secure* multitasking on this machine ^^^^^^^^ keep in mind >> If you want to realize reasonable memory segmentation (in my experience this >>is essential for TimeSharing) you MUST have a MMU. >Oh really? Then how do you explain the appearance of Minix (a Unix >look-alike) for the Atari ST? But look at the performance of that multitasking system. And, If I'd decide to write a real nasty program to run under Minix, the chance is 99% that I crash the WHOLE system with this program. Myself, I am a Minix user and I think I know what I'm talking about. Conclusion : Minix is a very nice software to use it for learning about time sharing, but it's useless for a *secure* (as I said above) every day multi(tasking|user) operation because it is definetely not reliable enough. You WILL have this problem with all multi tasking systems running on an unmodified ST. I think nobody would ever have the serious idea to use Minix to run an open access machine, for example, even if the hardware was sufficient (dialup lines, fast disk for the non-existent Minix swapper etc.). -- Thomas Cervera | UUCP: alderaan@tubopal.UUCP SysMan RKOpdp (RSTS/E) | alderaan%tubopal.UUCP@TUB.BITNET (saves $$$) D-1000 Berlin 30 | ...!pyramid!unido!tub!opal!alderaan Motzstrasze 14 | BITNET: alderaan%tub@DB0TUI11.BITNET
ralph@cc.brunel.ac.uk (Ralph Mitchell) (08/08/89)
In article <15706@watdragon.waterloo.edu> swklassen@dahlia.waterloo.edu (Steven W. Klassen) writes: >In article <652@opal.tubopal.UUCP> alderaan@tubopal.UUCP (Thomas Cervera) writes: >> >> What's all this about MultiTasking on the ST ? You don't have a MMU (not >>really and I think that's the worst failure in the ST's hardware architechture), >>so you are definetely not able to run a *secure* multitasking on this machine >>even if you want to - basta. All what you can call protected memory inside the >>[...] >Oh really? Then how do you explain the appearance of Minix (a Unix >look-alike) for the Atari ST? > >I have cross posted this to the Minix newsgroup. I thought you (Thomas) >might be interested in telling those who gave the ST multitasking >just why what they have done is not possible. Actually, he did say SECURE multitasking was not possible. i.e. One process address space is not protected against another process writing all over it. Ralph Mitchell -- JANET: ralph@uk.ac.brunel.cc ARPA: ralph%cc.brunel.ac.uk@cwi.nl UUCP: ...ukc!cc.brunel!ralph PHONE: +44 895 74000 x2561 "There's so many different worlds, so many different Suns" - Dire Straits "Never underestimate the power of human stupidity" - Salvor Hardin, Foundation
XBR2D78V%DDATHD21.BITNET@cunyvm.cuny.edu (MATHIAS GAERTNER) (08/08/89)
Well,
the MINIX-code is not the fastest and security is not the best, but it is not
the only multi-tasking system on this machine.
Think at the famous OS-9 or MIRACLE (not tested here!). They all work fine,
fast AND secure (at least OS-9).
So, good systems are possible even without a MMU!
M. Gaertner
TH Darmstadt, W. Germany
XBR2D78V@DDATHD21.BITNETpeter@ficc.uu.net (Peter da Silva) (08/09/89)
In article <21282@louie.udel.EDU>, XBR2D78V%DDATHD21.BITNET@cunyvm.cuny.edu (MATHIAS GAERTNER) writes: > Think at the famous OS-9 or MIRACLE (not tested here!). They all work fine, > fast AND secure (at least OS-9). > So, good systems are possible even without a MMU! OS-9 has one huge advantage over MINIX. It was designed for systems without an MMU, so it doesn't assume you can relocate logical zero, and it doesn't have to implement fork(). On the down-side it's totally non-portable outside the 6809/68000 world. -- Peter da Silva, Xenix Support, Ferranti International Controls Corporation. Business: peter@ficc.uu.net, +1 713 274 5180. | "The sentence I am now Personal: peter@sugar.hackercorp.com. `-_-' | writing is the sentence Quote: Have you hugged your wolf today? 'U` | you are now reading"
ralph@cc.brunel.ac.uk (Ralph Mitchell) (08/09/89)
In article <21282@louie.udel.EDU> XBR2D78V%DDATHD21.BITNET@cunyvm.cuny.edu (MATHIAS GAERTNER) writes: >Well, >the MINIX-code is not the fastest and security is not the best, but it is not >the only multi-tasking system on this machine. >Think at the famous OS-9 or MIRACLE (not tested here!). They all work fine, >fast AND secure (at least OS-9). >So, good systems are possible even without a MMU! I think we're not talking about the sort of security that stops a user attacking the filesystem or another user's files. We're talking about a process being confined to its own memory space. The Atari MMU doesn't keep track of which process owns which memory block, so any process could wipe out any other process's memory... Ralph Mitchell -- JANET: ralph@uk.ac.brunel.cc ARPA: ralph%cc.brunel.ac.uk@cwi.nl UUCP: ...ukc!cc.brunel!ralph PHONE: +44 895 74000 x2561 "There's so many different worlds, so many different Suns" - Dire Straits "Never underestimate the power of human stupidity" - Salvor Hardin, Foundation
sww@optima.optimage.COM (Stephan W.Wendl) (08/09/89)
When do people stop complaining about things that were not
intended. Minix was clearly meant to be a system for teaching
operatings systems and NOT to replace unix (tm), msdos, amigados,
MacLooser and other software crawling between chips.
It is like buying a bicycle and complaining why it doesn't get
you to the moon.
--
Stephan W. Wendl Optimage Chicago, Il 60606
(CompuServe) 300 W. Adams St., Suite 601
(72431,1232) uunet!{philabs,mcrware}!optima!sww
(312) 853-2637 FAX: (312) 782-9175swklassen@dahlia.waterloo.edu (Steven W. Klassen) (08/09/89)
In article <666@opal.tubopal.UUCP> alderaan@tubopal.UUCP (Thomas Cervera) writes: >>> If you want to realize reasonable memory segmentation (in my experience this >>>is essential for TimeSharing) you MUST have a MMU. >>Oh really? Then how do you explain the appearance of Minix (a Unix >>look-alike) for the Atari ST? > > But look at the performance of that multitasking system. > And, If I'd decide to write a real nasty program to run under Minix, >the chance is 99% that I crash the WHOLE system with this program. Myself, >I am a Minix user and I think I know what I'm talking about. > > Conclusion : Minix is a very nice software to use it for learning about >time sharing, but it's useless for a *secure* (as I said above) every day >multi(tasking|user) operation because it is definetely not reliable enough. >You WILL have this problem with all multi tasking systems running on an >unmodified ST. "Although MINIX was first implemented on the IBM PC/XT/AT familiy, it was written with portability in mind. We considered it a challenge to test the portability, and used the Atari ST as the target machine for a number of reasons. The ST is a popular machine with a good price/ performance ratio, and attracts a different class of users. The ST uses the Motorola 68000 processor, as several other popular micros do, so that a port to the ST could serve as the starting point for ports to the Apple Macintosh and Commodore Amiga. LASTLY, THERE IS A WIDESPREAD BELIEF THAT UNIX, AND THEREFORE MINIX, REQUIRES THE SUPPORT OF A MEMORY MANAGEMENT UNIT (MMU). PROVING THE OPPOSITE HAS BEEN ONE OF OUR DRIVING FORCES." (excerpt from Intro to Minix ST manual) You emphasize that MINIX ST is not secure and claim this is due to the lack of the MMU. I agree that MINIX ST is not secure but claim that this is not due to the lack of an MMU but due to the fact that Mr. Tanenbaum wanted to keep things simple. To support this note that MINIX is not particularly secure on the IBMs either even though they do have a (sort of) MMU. As for the security of other attempts at multiprocessing (eg. MX2), I have not tried any of them so I really can't comment on them. Finally, I agree with you that the Atari ST hardware is not meant for multitasking. My dissagrement is that I claim this makes multitasking difficult and inefficient (compared to a machine that does support it in hardware) BUT NOT IMPOSSIBLE. Let me close with the conclusion which I have been trying to get accross: 1) MULTITASKING IS USEFUL, EVEN ON A SINGLE-USER MACHINE 2) MULTITASKING IS POSSIBLE WITHOUT A GREAT DEAL OF EXTRA HARDWARE 3) MINIX AND MX2 ARE EVIDENCE THAT ATARI USERS WANT MULTITASKING 4) HENCE ATARI CORP SHOULD GIVE US MULTITASKING *WITH*THE*HARDWARE*TO* MAKE*IT*EFFICIENT. Steven W. Klassen Computer Science Major University of Waterloo
rob@kaa.eng.ohio-state.edu (Rob Carriere) (08/10/89)
In article <666@opal.tubopal.UUCP> alderaan@tubopal.UUCP (Thomas Cervera) writes: > And, If I'd decide to write a real nasty program to run under Minix, >the chance is 99% that I crash the WHOLE system with this program. Myself, >I am a Minix user and I think I know what I'm talking about. I'll gladly concur until you supply evidence to the contrary. :-) > Conclusion : Minix is a very nice software to use it for learning about >time sharing, but it's useless for a *secure* (as I said above) every day >multi(tasking|user) operation because it is definetely not reliable enough. >You WILL have this problem with all multi tasking systems running on an >unmodified ST. Yup. You will also have the _exact_same_ security problem with any task switcher on an unmodified ST. At the very least the taskswitcher must keep part of itself in memory. I can trash that from my program. You will have the same problem with a RAM-disk. This is not an argument against multitasking and for task switching because it applies with equal force to both. SR