Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!cs.utexas.edu!rice!uupsi!grebyn!ckp
From: ckp@grebyn.com (Checkpoint Technologies)
Newsgroups: comp.sys.amiga.tech
Subject: Re: MMU + A3000 + AmigaOS2.0 == Non-crashing system?
Message-ID: <20927@grebyn.com>
Date: 2 Aug 90 14:31:27 GMT
References: <2489@clinet.FI> <20889@grebyn.com> <6405@wolfen.cc.uow.oz>
Reply-To: ckp@grebyn.UUCP (Checkpoint Technologies)
Organization: Grebyn Timesharing, Vienna, VA, USA
Lines: 39

In article <6405@wolfen.cc.uow.oz> zahra@wolfen.cc.uow.oz (Andrew Zahra Telecom) writes:
>In article <20889@grebyn.com>, ckp@grebyn.com (Checkpoint Technologies) writes:
>> 
>> Yes, there's been a lot of traffic in the comp.sys.amiga.xxx groups
>> about this.  Unfortunately, I haven't heard a workable solution for
>> existing applications, I can't think of one myself, and many net.folk
>> whose opinions I respect have claimed it can't be practically done.
>> 
>> Therefore, the way to get MMU protection for your applications is to
>> abandon application binary compatibility; and if you're going to do
>> this anyway, then why not just use Unix?
>> -- 
>
>	Wouldn't it be possible to phase in mmu support by having a mechanism to
>let the os know if your program can handle having an mmu protect things from it.This way the things would progressively become more stable as more of these new
>prgs appear - old prgs would just have their protection mask set to have access
>to all memory and they'd never know the difference...

I think this is grand.  In fact, Commodore seems to be planning this,
because they already have plans to implement Virtual Memory.
Unfortunately VM does not necessarily imply "protection". It offers only
a larger virtual memory area than available physical memory provides.

My definition of "Protection": Where each program has a unique
virtual address space, and where the address space of all other programs
is unaddressable, except in such case that two tasks formally agree to
share some memory space and make this known to the OS.  When any program
addresses memory which is not in it's virtual address space, it bombs.
But also note: even though other programs have been protected by this
trap, the OS itself has not been unless it has knowledge of all the
resources owned by the program, and can reclaim them.  Therefore
"Protection" implies "resource tracking".


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