[NTLUG:Discuss] CPU History

[Steve Baker]

Darin Smith wrote:

> I've run Linux on nothing but AMD processors since their 486 clones.
> 
> I've used a 486-66DX, 5x86, K6, K6-II, and now a 1.3 GHz Athlon.
> 
> Never once had a problem.

It's good that you never had a problem with AMD - and it's not like
Intel CPU's havn't had bugs over the years...but AMD CPU's are certainly
no better than Intel's from a design reliability perspective.

I had terrible problems with the AMD 450MHz K6-II CPU - it had a
subtle hardware design error that meant it wouldn't compile things
reliably.  I'd often have to type 'make' a half dozen times to get
a complicated program to compile.  If I wanted to compile something
*REALLY* complicated like the kernel or Xfree86, I'd have to type:

   while ( 1 )
     make
   end

...and leave it running overnight!

The hardware bug was that the CPU would sometimes execute an instruction
twice in succession.  It was a very rare event - and executing most machine
code instructions twice causes no harm at all.

Hence, the bug somehow managed not to show up under Windoze - except
in carefully contrived programs written to show off the problem.  The
only program that ever exhibited a problem under Linux was gcc.  This
meant that many people believed it was a gcc software bug until someone
finally tracked it down.

There were many FAQ's written about it at the time.  Here is one of the
better ones:

     http://membres.lycos.fr/poulot/k6bug.html

AMD originally offered to replace the CPU if people found they
had problems - but when I tried to take them up on that offer,
they refused because "the problem doesn't affect Windows programs
and there is a reasonable work-around for Linux users".

Their work-around is to not install more than 32Mb of RAM - or to
switch over to Windoze!?!

Oh - just *great*.

The most annoying thing is that the problem was originally discovered,
documented and reported to AMD in the early days of the 200MHz part - yet
they didn't fix it in either the 300 or 450MHz devices.

I gave up on AMD at that point.  Since then I've only used Intel CPU's
and I havn't had any problems since then.

I'm not a huge fan of either company - but I don't think either of
them has a clear lead over the other in terms of CPU quality.
---------------------------- Steve Baker -------------------------
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