A machine which has been very stable recently started giving me
problems.  gcc starts crashing or reporting wierd errors, other programs
randomly SEGV, etc.  It's a little like the sun3 pmap bug, if you're
familiar with that. Starts out fine, and things slowly goes downhill.

The change was sudden and drastic, and coincided with the installation
of a program that uses mmap() heavily -- large regions of anonymous
memory, for long periods of time, multiple processes accessing it.  When
I disable this software, the machine is fine. 

So: either there is a VM bug trigered by all this activity, or there is
a problem with memory (or maybe cache) that doesn't get hit, or not
often, except under the memory access patterns caused by this software.
I can pound on the machine fairly hard without the program, and all is
well.

The machine is a P166MMX, Asus TX97-XEA with one 32M DIMM (from a vendor
who knows what DIMMs work), and either 1.3 or 1.3.1 from the same config
file.  It seems to be a little worse [goes insane a little more rapidly]
with 1.3.1. 

So, can anyone recommend some goof freeware memory test software for
PCs? Something that runs under DOS is fine.