Advanced Micro Devices Inc (AMD)

[chipguy]

But both P4 and Athlon seem to be quite "testable."

All chips are testable to an arbitrary degree, the question is what to test for since testing
for everything is absolutely out of the question. The I2 has been in production for 9 months
while P4 and K7 microarchitecture chips have been in production for years so their test
coverage is better understood. IIRC AMD had an issue with some K7s producing incorrect
results for certain SIMD code sequences a while back. That sounds a lot like the I2 bug.