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From: phil@amdcad.UUCP (Phil Ngai)
Newsgroups: comp.sys.m68k
Subject: Re: Comparing 68xxx's; really TLB misses
Message-ID: <14561@amdcad.UUCP>
Date: Sun, 1-Feb-87 15:15:09 EST
Article-I.D.: amdcad.14561
Posted: Sun Feb  1 15:15:09 1987
Date-Received: Sun, 1-Feb-87 22:49:30 EST
References: <809@imagen.UUCP> <561@elmgate.UUCP> <1090@msudoc.UUCP> <1701@hoptoad.uucp>
Reply-To: phil@amdcad.UUCP (Phil Ngai)
Organization: Advanced Micro Devices, Sunnyvale, California
Lines: 34

In article <1701@hoptoad.uucp> gnu@hoptoad.uucp (John Gilmore) writes:
>The 68012 is a version of the 68010 which has a 31-bit address bus,
>packaged in a chip carrier (or pin grid array?).  It's actually the
>same chip, but the package has more wires coming out.  The 68010
>couldn't add more wires because it was designed to be plugged in
>anywhere a 68000 goes.  This was a stopgap for people who wanted a
>large virtual address space (>16 megs) but couldn't wait for the
>68020.  I don't know any popular machine that uses them.

I was going to say, you must mean physical address, not virtual, but
then I remembered the 68K puts out virtual addresses since it has
no MMU.

>The 68030's MMU is the mediocre one that they build for the 68020; it
>does slow Vax-style page table lookup in main memory and has more features
>and options than you ever cared to read about.

Any prediction on how fast a TLB miss is handled? I seem to recall the
VAX 780, which does it in hardware, takes about 4 microseconds while
MIPS, which does it in software, takes from 1-2 microseconds for a
micro-TLB miss. I don't know how long a regular TLB miss takes. Many
people are shocked at the idea but looking at the bottom line, "how
long does it take", software TLB refill doesn't seem like such a bad
idea. 

Any one know how fast the other chips are at TLB refills? Intel, NSC,
Fairchild, which I assume do it in hardware?

-- 
 They also surf who only stand on waves.

 Phil Ngai +1 408 982 7840
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