[NTLUG:Discuss] AMD K6 200 vs Pentium MMX 200

[Pete. Koren]

Steve Baker wrote:
> 
> THere is a hardware bug in at least some AMD K6-200's.  This bug
> only seems to show up under Linux - and had only been seen to affect
> the GNU C/C++ compilers - and only then if you have more than 32Mb RAM.
> 
> I have a 266MHz AMD - and when I found there was a problem (the GNU
> compiler guys told me it was a hardware bug), I called AMD. They
> claimed that the problem only affected 133MHz parts and that it
> was fixed in the 200's and later.
> 
> However, I definitely have the bug - and several web sites out there
> agree with me that it affects the 233's and 266's.  When I upgraded
> to 450MHz AMD, the problem went away.
> 
> AMD also claimed that the bug only occours when recompiling the kernel,
> but the truth is that it can happen on any compile - and hits you about
> one in a hundred compiler runs.  Unfortunately, I'm compiling a program
> that's composed of about 50 files - so about half the time, my program
> will fail to compile when I do a clean rebuild.  Re-running the same
> compile again would work half the time....very frustrating...especially
> when trying to install other people's source code.
> 
> The bug is something to do with execution of prefetched instructions
> from cache. When there is more than 32Mb RAM, and when the program has
> data stored at address 32Mb+X being accessed at the same time as an
> instruction from address X, the cache gets confused and can produce the same instruction twice in a row under certain timing situations.  Many
> programs survive having an instruction executed twice in a row - and it's
> quite unlikely that this particular set of circumstances should happen
> but the Linux C/C++ compiler seems pretty vulnerable.
> 
> There is supposed to be a kernel patch to reduce the instance of the
> problem by trying never to allocate memory to a program at both X and
> 32Mb+X....but it didn't fix the problem for me - and isn't claimed to
> be perfect.
> 
> So, I found owning an AMD to be a *SERIOUS* pain.  If you plan to
> compile programs - and need >32Mb - get the Intel part.
>

I am now replacing my old broken AMD K6 200 system
because it crashes on long installs, both Linux OS
installs and Winblows 98.

Regards,

Peter Koren