Mystery CPUID Bit
Summary
The OS/2 Museum post documents an undocumented CPUID bit (bit 18) in leaf 80000001h observed on Athlon Thunderbird/Duron CPUs. It discusses potential meanings (ECC capability, MP capability), cites public docs and sandpile.org, and notes ongoing community discussion that revealed inconsistencies in AMD documentation surrounding bit 18 and bit 19, illustrating challenges in hardware documentation history.