Path: utzoo!lsuc!hcr!edwin
From: edwin@hcr.UUCP (Edwin Hoogerbeets)
Newsgroups: comp.sys.amiga.tech
Subject: Address Space on the Amiga (was Re: Need info on exceptions)
Message-ID: <3859@hcr.UUCP>
Date: Mon, 29-Aug-88 11:07:59 EST
Article-I.D.: hcr.3859
References: <8808272322.AA03740@cory.Berkeley.EDU> <125@fishpond.UUCP>
Reply-To: edwin@hcrvax.UUCP (Edwin Hoogerbeets)
Organization: HCR Corporation, Toronto
Lines: 36
Keywords: Queen's -, Florida -s
Summary: 

In article <125@fishpond.UUCP> fnf@fishpond.UUCP (Fred Fish) writes:
>In article <8808272322.AA03740@cory.Berkeley.EDU> dillon@CORY.BERKELEY.EDU (Matt Dillon) writes:
>>: [somebody besides Matt writes]
>>:				An idea central to the Amiga
>>:is that an address in any tasks address space is not a virtual 
>>:address but a physical memory address. That means that you can hand 
>>:a pointer off to another task and it will be valid in THAT tasks's address
>>:space.
>>	Yes, this *IS* a nice idea.
>Personally I think this is the single biggest problem with the Amiga.  

I agree with Fred. The idea of a process is that the situation should
look, to the process itself, as if it is the king of the CPU. No-one
else is on this machine. If communication should occur, then you should
assume the process you are talking to is on another machine (when it
really is on the same one, but hey, let's be sneaky and not tell the
first process about it!) This is the theoretical "higher concept".

One example of the disadvantage of this "pointer passing in msgs" is
that it makes things difficult to do networking at the OS level. Making
message passing transparent on a network is difficult because you don't
know if a pointer to some memory is being passed. (Same as the problem
with fork() on the 68000/no mmu about not knowing which data are
pointers)

However, I can see how no mmu/memory protection/etc. can appeal to
hackers. "Do what I say, and I'll be happy." Matt and others have
produced some very nice software because of it. Also, passing messages
and data structures by pointer is FAST. Also, queues are a lot shorter
because you are only passing 32 bit quantities.

I just wonder what's going to happen on the 2500 and 3000...


Edwin (Deepthot) Hoogerbeets
uunet!utai!utcsri!hcr!edwin