Path: utzoo!attcan!uunet!husc6!cs.utexas.edu!oakhill!tomj From: tomj@oakhill.UUCP (Tom Johnson) Newsgroups: comp.sys.mac Subject: Re: When will MacOS get virtual memory? Summary: The 68000 is NOT "flawed" Keywords: 68000 MMU Virtual Memory Message-ID: <1526@oakhill.UUCP> Date: 4 Oct 88 16:00:15 GMT References: <5624@zodiac.UUCP> <76000290@p.cs.uiuc.edu> Reply-To: tomj@oakhill.UUCP (Tom Johnson) Organization: Motorola Inc., Austin Tx. Lines: 48 In article <76000290@p.cs.uiuc.edu> gillies@p.cs.uiuc.edu writes: > >The sad thing is, the vast majority of Macintoshes in this world >cannot support virtual memory. This is because the 68000 chip has a >design flaw that doesn't allow virtual memory to be implemented. ---- >.... > >Don Gillies, Dept. of Computer Science, University of Illinois >ARPA: gillies@cs.uiuc.edu UUCP: {uunet,ihnp4,harvard}!uiucdcs!gillies I have to take exception to this statement. This is like saying that Henry Ford's Model T was flawed since it didn't have an 8 cylinder engine and mechanical air conditioning (opening the windows doesn't count :>)). In 1979 when the 68000 was first introduced, it was the largest commercially produced die ever attempted by man. For the first time, we were given internal 32-bit MPU features while the rest of the world was still thinking 8-bits. We were given a large number of general purpose registers while the rest of the world still had to struggle with dedicated registers. After Motorola **sucessfully** began producing the 68000, the designers went back to the drawing tables and started adding extra features: full virtaul memory and virtual machine suport and loop mode in the 68010; 32-bit ALU's, on-chip instruction cache, and full 32-bit external bus support in the 68020; on-chip data cache, on-chip paged MMU, synchronous bus, burst mode, and on-chip Harvard architecture in the 68030. The Motorola High End design team has spent the last 9 years carefully executing a plan to give the user community the highest possible performance given a moving fabrication technology target. I don't know why Apple chose to use the 68000 in the original toaster Mac's rather than the 68010, but I would assume that it had a lot to do with pricing. Motorola took a huge gamble introducing a microprocessor which broke with the industry convention (set by Intel) of always introducing MPUs that were completely compatible with existing families (8080-->80188-->80186-->80286--> 80386-->... vs 6800-->6801-->6805-->68HC11 ||| 68000-->68010-->68020-->68030 -->680x0-->...). I think most readers of this group would agree that Motorola made the right choice in this respect. Let's quit talking about the "flawed" 68000 (or 67999 as one poster stated a few months ago), and just be glad that Motorola has given us what we all wanted...a very high performance, orthogonal, easy to program, upward compatible MPU family that is STILL the metric by which most, if not all, other microprocessors are judged. _____________________________________________________________________________ |Disclaimer: The views stated above are my own and do not necessarily | | reflect the views of Motorola. | | | |tomj@oakhill.UUCP Tom Johnson | |(512)440-2143 Motorola High-End Marketing | | Austin, TX | |_____________________________________________________________________________|