Mystery Cpuid Bit
2 days ago
- #CPUID
- #AMD Athlon
- #ECC Memory
- The author discovered an undocumented CPUID bit 18 in an Athlon 1200 Thunderbird CPU, which was initially unknown and reserved according to official AMD documentation.
- Research revealed that bit 18 was intended to indicate ECC (Error-Correcting Code) capability for AMD K7 processors, although this was not officially documented, while bit 19 indicated MP (multi-processing) capability.
- Historical context suggests that AMD initially supported ECC in Slot A Athlons but may have dropped it for Socket 462 models, with confusion in documentation leading to bits 18 and 19 being misinterpreted over time.
- The author speculated that some Athlon Thunderbird and Duron models with bit 18 set might actually support ECC, but verifying this was difficult due to hardware limitations and lack of documentation.
- Discussions included references to elusive AMD BIOS guides, potential links to debug modes or overclocking features, and the role of chipsets in ECC support, highlighting the complexities of historical hardware documentation.