Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!pasteur!ames!oliveb!amiga!cbmvax!daveh
From: daveh@cbmvax.UUCP (Dave Haynie)
Newsgroups: comp.sys.amiga.tech
Subject: Re: MEMF_PHYSICAL?
Message-ID: <7060@cbmvax.UUCP>
Date: 7 Jun 89 17:46:39 GMT
References: <8906030123.AA14671@jade.berkeley.edu>
Organization: Commodore Technology, West Chester, PA
Lines: 36

in article <8906030123.AA14671@jade.berkeley.edu>, 451061@UOTTAWA.BITNET (Valentin Pepelea) says:

>> But most of the time it's simple things,
>> like not deallocating memory, or overwriting OS structures with a runaway
>> pointer. These problems simply do not arise on systems with private
>> address spaces, or even on systems with a single address space but
>> each task limited to writing in the memory that belongs to it.

> Whoa! Now he is comparing an operating system which has resource tracking with
> one which does not. That is ridiculous. It is obvious that when memory
> protection is implemented on the Amiga, resource tracking will have to be added
> so that crashing programs may free up the requested resources. In a separate
> address space operating system, resource tracking has to be implemented too,
> and it is just as difficult to implement, if not more.

I agree, there's nothing inherently safer about systems with private address
spaces vs. those with a single address space.  Equal protection can be added
to each; the MMU doesn't care.  Most of the single-space problems we have in
the Amiga, like overwriting structures, etc. are purely a problem because we
don't have protection.  Either protected system would drop you out with an
access violation; the memory model has nothing to do with it.  About the
only obvious advantage of the private-space-per-task model is that it makes
memory allocation tracking much easier to do, since you need only allocate
memory contiguously, and thus keep track of only the start and finish of
your allocated memory, vs. the list that a single-space OS will need for
each task.  But memory tracking is simple, anyway (it could even be added to
AmigaOS on a per-task basis easily), it's the tracking of other resources
that both systems have to deal with properly, and that's got nothing to do
with the memory space model.

> Valentin

-- 
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