Athlon 64: How AMD Turned the Tables on Intel On September 23, 2003, AMD released the Athlon 64, a groundbreaking CPU that extended the x86 architecture to 64 bits—something Intel was reluctant to do. This shift forced Intel to ultimately copy AMD’s design, reversing the usual narrative of Intel leading and AMD following. Why Intel Didn’t Want to Go 64-bit Initially Legacy Architecture: x86 originated from an 8-bit CPU from 1972 (Datapoint), evolving through 16-bit to 32-bit. Backward compatibility was a key strength, allowing decades-old software to still run. Intel’s Strategy: Intel sought a fresh start for 64-bit computing without legacy baggage, aiming for a faster, more efficient architecture that could scale higher clock speeds. Itanium: Intel’s new 64-bit architecture, Itanium, launched in 2001. Though innovative, Itanium was niche and saw little mainstream success, especially with Windows. AMD’s Risky Bet AMD chose to extend x86 to 64 bits, maintaining full backward compatibility with 32-bit applications and hardware. Their rationale: Market Appeal: A 64-bit processor that could run 32-bit software at full speed offered an easier adoption path. Long Transition: Like the decade-long switch from 16-bit to 32-bit, AMD believed a gradual transition would win over customers. Windows Support: AMD anticipated Microsoft would support 64-bit x86 Windows as they had for Itanium. Impact of Athlon 64 Backward Compatibility: Users could run existing 32-bit Windows and applications immediately, easing adoption. Performance: Athlon 64 was a strong 32-bit CPU, outperforming Intel’s CPUs at equivalent clock speeds while consuming less power—a critical factor for data centers. Enterprise Adoption: Dell incorporated AMD CPUs, including Athlon 64 and Opterons, into servers and desktops, breaking Intel’s exclusivity. Market Shift: Intel was forced to adopt a compatibility mode and clone AMD’s instruction set as Intel64 in 2004. Itanium was eventually discontinued in 2020. Legacy and Significance AMD’s success with Athlon 64 marked the second time the company overtook Intel in CPU innovation (after the original Athlon in 1999). It demonstrated that extending x86 with 64-bit support was viable and could reshape CPU competition. The rivalry between AMD and Intel has continued with each leapfrogging the other in successive CPU generations. --- Additional Notes The article’s author, Dave Farquhar, is a computer security professional with deep expertise in retro computing and IT. Historical context includes the fading of other CPU competitors like Transmeta and Cyrix around that time. Comments reflect curiosity about future CPU instruction set extensions and AMD’s architectural decisions. --- This summary captures how AMD’s Athlon 64 changed the x86 CPU landscape by extending 64-bit capability within the legacy architecture, forcing Intel to abandon its alternative Itanium platform and adopt AMD’s design.