Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!husc6!hao!ames!oliveb!amiga!cbmvax!daveh
From: daveh@cbmvax.UUCP (Dave Haynie)
Newsgroups: comp.sys.amiga
Subject: Re: MY Wishlist for A3000
Message-ID: <2761@cbmvax.UUCP>
Date: Fri, 13-Nov-87 15:35:52 EST
Article-I.D.: cbmvax.2761
Posted: Fri Nov 13 15:35:52 1987
Date-Received: Sun, 15-Nov-87 11:42:49 EST
References: <5887@jade.BERKELEY.EDU>
Organization: Commodore Technology, West Chester, PA
Lines: 43

in article <5887@jade.BERKELEY.EDU>, mwm@eris.BERKELEY.EDU (Mike (My watch has windows) Meyer) says:
> Keywords: Commodore A3000 Do it RIGHT!

Oh, no, here I go again....

> <I don't need a 68030, or even a 68020.  I need a 68010 so I can have
> <the VM I require.

> The 68000 will support memory mapping just fine.
> It has problems with demand paging - it doesn't even *have* a page
> fault, much less do it right :-). It does have a line to use when it
> tries to address memory that's not there. 

No, not really.  It has a few exceptions that can be used for this, but
none of them work for what you want.  That's certainly why "68010" 
appears above instead of "68000".

> The stack frame doesn't have
> sufficient information to let the OS restart/continue (choose one,
> depending on religion) the faulting instruction after paging things
> in. These didn't stop the sufficiently dedicated/devious from doing
> demand paging on the 68000 (or two of them, in some cases).

Well, I've seen the Apollo scheme.  They use two 68000s, the second one
tells the first one what it was doing when the page fault occurred.  It
was a reasonable kludge back then, but that was before the '010 existed.
Since the '010 is a pin-compatible replacement for the '000, there's 
absolutely no problem today.  And you still need an MMU.

> If you're going to do demand paging, real memory quits affecting
> what/how much you can run, and just makes things go faster.

Sure enough.  Like, all my Amigas have more real memory than any of our
Apollos, and appear to run faster, even though the Apollos have much
higher clock speeds.  A DN3000 would change this, certainly, though that
has an '020 and does virtual memory right.  And probably has more on-board
RAM as well.

> 	<mike
-- 
Dave Haynie     Commodore-Amiga    Usenet: {ihnp4|caip|rutgers}!cbmvax!daveh
   "The B2000 Guy"              PLINK : D-DAVE H             BIX   : hazy
    "Computers are what happen when you give up sleeping" - Iggy the Cat