Nopl

During research for my Geode Repair projects, I found something incredibly weird so this page is my attempt to write it down.

Background

The AMD Geode LX800 CPU is an incredibly strange CPU.

It implements the following instruction sets:

• Pentium (i586)
• Pentium Pro (i686)
• MMX
• Extended MMX
• 3DNow!
• Enhanced 3DNow!

Notably the machine does not support PAE (Physical Address Extension). This may be why the CPUID identifies as family 5 (Pentium), not family 6 (Pentium Pro). This is all according to my reading of the AMD Geode LX Processors Data Book.

In contrast, some CPUs like the VIA C3 marked their CPU as family 6 without implementing the instruction set specified in the Pentium Pro Family Developer's Manual Volume 2. Most notably the 'CMOV' instruction.

But in theory, you could run an i686 system on the Geode without PAE. In practice it's a bit more complicated.