Athlon 64 at 23: How AMD Forced Intel to Copy Its 64-bit x86 Design

By Indie Kings | September 25, 2026

Updated September 25, 2026: On September 23, 2003, AMD released the Athlon 64, the first 64-bit x86 CPU. Computer security professional and retro computing writer Dave Farquhar, in a retrospective marking 23 years since the launch, argues the significance was not the 64-bit width itself but that AMD forced Intel to abandon its clean-break plan and copy AMD's approach instead.

Source: This article is based on Dave Farquhar's history piece at The Silicon Underground, published September 22, 2026.

Why Intel did not want 64-bit x86

By 2003, x86 carried decades of accumulated baggage. It was a 32-bit architecture extended from a 16-bit one, which had itself been extended from an 8-bit design that in 1972 originated at Datapoint rather than at Intel.

That history is the reason x86 won, not a reason to celebrate it. Backward compatibility is what made porting 8-bit applications to x86 cheap in the early 1980s, which is one of the reasons IBM chose the Intel 8088 for the original Model 5150 PC. Those early DOS applications still ran on modern systems decades later.

One point in the source is worth keeping straight, because it is often garbled. The inability to run 16-bit applications inside 64-bit Windows was a decision made by the operating system, not a limitation of the CPU.

Intel's position was that it could start over. A clean 64-bit design free of compatibility constraints could be faster and more efficient, and in theory scale to higher clock speeds. It would also be encumbered by enough patents that a competitor could not clone it for roughly two decades. Farquhar's paraphrase of the attitude, from Tracy Kidder's The Soul of a New Machine, is that Intel did not want to just put a bag on the side of x86.

AMD's bet and its downside case

AMD's problem in 2003 was concrete. If Itanium caught on, AMD's future as a CPU company was effectively over, short of becoming an instruction-set licensee. Transmeta was still in the picture, and Cyrix was fading but not gone.

AMD could see that Itanium was not catching on. It had niches, but Windows on Itanium was a non-starter, badly enough that The Register nicknamed it "Itanic".

So AMD extended x86 anyway, accepting the architectural inelegance. The reasoning was about demand, not elegance. Backward compatibility had always sold, so the plan was to make the 32-bit-to-64-bit transition feel like the 286-to-386 transition rather than a hard cut. Users could run 32-bit Windows and 32-bit applications at full speed until they were ready, and keep doing so inside 64-bit operating systems as long as needed.

The framing Farquhar gives is a two-sided bet. The market would tolerate lower 64-bit performance in exchange for much better 32-bit performance today, and Microsoft would take the risk on 64-bit x86 having already taken it on Itanium.

• Worst case: AMD64 becomes a vestigial extension like 3DNow, technically present and commercially irrelevant.
• Best case: AMD leapfrogs Intel, because it starts from an installed base instead of an empty one.

Why it actually worked

The 64-bit transition took about as long as AMD expected. Farquhar's own recollection is that in late 2005, administering bundled antivirus software for Charter Communications, 64-bit support requests arrived roughly weekly. When he finally bought an Athlon 64 in 2011, native 64-bit software was still scarce enough that he briefly switched browsers, which was then a meaningful signal of a software gap.

That is the part of the story most retellings skip. The hardware arrived first and the software caught up slowly, and the compatibility promise is what made the wait tolerable rather than disqualifying.

The data centre turn

The decisive shift was not gaming or desktop performance. Farquhar argues the Athlon 64 worked because, despite its name, it was an outstanding 32-bit CPU: faster than Intel at the same clock rate and lower power.

Power was the lever into the data centre, and the brand problem was real. Dell was an exclusively Intel vendor for years, to the point where AMD co-founder and longtime CEO Jerry Sanders said he could not sell Michael Dell an AMD K6 no matter what he tried. The Athlon 64 was what made Dell relent, and Dell then put AMD parts in servers, which would have been deeply controversial a few years earlier.

Farquhar's account is that replacing Prescott-based servers with AMD64 was not universally popular, but the difference was visible standing behind the racks. Uptime metrics slightly favoured AMD and performance metrics favoured AMD more clearly. A relative at HP reportedly told him enterprise customers were buying AMD64 specifically for power efficiency.

Intel cloning AMD64

In 2004 Intel wrote off Itanium and cloned AMD64, calling it Intel64. The source is careful about the legality here, and so should any retelling be. The agreements permitting AMD to use the x86 instruction set were reciprocal and gave Intel the rights to the AMD64 instructions, so there was nothing illegal about what Intel did. Itanium continued in specialised applications before Intel quietly discontinued it in 2020.

The pattern Farquhar identifies is oscillation rather than a permanent reversal. One company leads for a generation or two, positions swap, and the result looks much like the 1999 original Athlon, when AMD outperformed Intel for the first time. His framing is that the Athlon 64 was the second time, and the first time AMD was innovating rather than positioning a high-clocked 486 as a Pentium equivalent.

What the history does not settle

This is a retrospective, not a benchmark study, and a few boundaries are worth marking.

• No performance data. The source offers no clock speeds, benchmarks, or power measurements for Athlon 64 parts. The 32-bit superiority claim is the author's characterisation.
• Deployment anecdotes. The enterprise claims come from one administrator's direct experience and a relative's account of HP sales. They are illustrative, not a sample.
• No causation proof on Microsoft. That Microsoft built Windows x64 because of the Athlon 64 is the author's reasoning about incentives, not a documented decision.
• No transition-cost accounting. The long, awkward 32-bit to 64-bit software period is described but not measured.

FAQ

When was the Athlon 64 released?
September 23, 2003, as the first 64-bit x86 CPU.

Why did Intel not want to extend x86 to 64 bits?
Intel wanted a clean-slate design free of backward-compatibility constraints, which was faster in theory and protected by patents that would keep competitors out for years.

Was 64-bit Windows unable to run 16-bit applications because of the CPU?
No. The source is explicit that this was an operating system design decision, not a technical limitation of the processor.

Was Itanium a commercial failure?
It found niches, but Windows on Itanium was a non-starter, to the point where The Register called it "Itanic". Intel discontinued it in 2020.

Why was backward compatibility the winning argument?
Because it let users delay the 64-bit upgrade at full 32-bit speed, turning a hard architectural break into a gradual transition that buyers could stage.

Did Intel break the law by making Intel64?
No. The x86 instruction-set agreements were reciprocal and gave Intel rights to the AMD64 instructions, so the clone was legal.

Bottom Line

The Athlon 64 is usually told as a story about a faster CPU. Farquhar's reading is sharper: it was a strategy story about refusing to be architecturally elegant in exchange for being adoptable. Intel's clean break was the technically purer path and it lost, because it started from zero while AMD started from every 32-bit PC ever sold. The 2004 Intel64 clone is the visible proof that the compatibility argument won, and the data centre power story is why it turned into market share. The launch was not the hard part. Surviving a decade of slow 64-bit software adoption was.

Source: Athlon 64: How AMD turned the tables on Intel, by Dave Farquhar, The Silicon Underground

Related: AMD versus Intel CPU market share