Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!shadooby!eecae!netnews.upenn.edu!rutgers!att!mtuxo!mtgzz!drutx!druwy!dlm
From: dlm@druwy.ATT.COM (Dan Moore)
Newsgroups: comp.sys.amiga
Subject: Re: UNIX vs. Amiga speeds
Message-ID: <3945@druwy.ATT.COM>
Date: 30 Mar 89 15:59:33 GMT
References: <6411@cbmvax.UUCP>
Organization: AT&T, Denver, CO
Lines: 26

in article <6411@cbmvax.UUCP>, andy@cbmvax.UUCP (Andy Finkel) says:
> As I recall, the 68000 has a bit of trouble recovering from
> an address error.  (not enough state info saved). 
> This was fixed in the 68010.  (wasn't there a 68000 computer
> that used 2 68000s to get around this one ?)

	The real limitation on the 68000 is lack of state information
after a buss error.  The MMUs all generate buss errors when an access to
unmapped RAM occurs, that's so the OS can swap a page to/from disk.

	Motorola sent out a tech report describing how to use two 68000s
and a 68451 MMU.  The first 68K ran the user programs, instead of
causing it to buss error the 68451 would wait state it and cause the
second 68000 to take over.  The second 68000 would then fix the memory
fault by swapping to/from disk and then allow the first 68000 to resume
execution of the user code.

	I wonder if anyone ever really built a system that worked that
way.



				Dan Moore
				AT&T Bell Labs
				Denver
				dlm@druwy.ATT.COM