Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!sun-barr!oliveb!amiga!cbmvax!daveh
From: daveh@cbmvax.UUCP (Dave Haynie)
Newsgroups: comp.sys.amiga.tech
Subject: Re: MEMF_PHYSICAL?
Message-ID: <7097@cbmvax.UUCP>
Date: 19 Jun 89 15:04:06 GMT
References: <1265@pkmab.se>
Organization: Commodore Technology, West Chester, PA
Lines: 28

in article <1265@pkmab.se>, ske@pkmab.se (Kristoffer Eriksson) says:

> In a system with a monolithic kernel (like UNIX), I could imagine a simple
> way to protect the kernel from the user programs without protecting the user
> programs from each other, but the Amiga has a lot of separate tasks in stead
> of a single kernel, so that does not apply. And it would only be half a
> protected system as I see it, anyway.

If you give each task under Exec it's own MMU map (same basic idea as UNIX),
it would be fully possibly to protect every task from every other one.  Of
course, once you start using messages, you have to allocate some memory that's
shared between tasks, and that leaves it open for a mutant task to bugger up
someone else's messages.  Though you might expect that, until a task asks for
shared memory or the use of the messaging system, it's not given access to 
any shared memory.  It wouldn't perhaps be as bullet proof as UNIX, but it
would be fairly tough.  Both UNIX and AmigaOS count on an OS function to do
the task switching -- it's not like one task passes off to another without
help from the OS (things like math chips wouldn't work correctly if this were
happening).

> -- 
> Kristoffer Eriksson, Peridot Konsult AB, Hagagatan 6, S-703 40 Oerebro, Sweden
> Phone: +46 19-13 03 60  !  e-mail: ske@pkmab.se
> Fax:   +46 19-11 51 03  !  or ...!{uunet,mcvax}!sunic.sunet.se!kullmar!pkmab!ske
-- 
Dave Haynie  "The 32 Bit Guy"     Commodore-Amiga  "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: D-DAVE H     BIX: hazy
              Amiga -- It's not just a job, it's an obsession