The encyclopedia · Software & IT · Technical decision · 1999–2004
AMD's x86-64 won 64-bit computing by extending x86, not replacing it
AMD added 64-bit instructions to the existing x86 ISA so old software still ran; Intel's incompatible Itanium stalled, and Intel ended up cloning AMD's design.
Advanced Micro Devices (AMD) · Intel
The solution
Intel's 64-bit strategy was Itanium, a brand-new architecture. It shipped in 2001 but ran existing 32-bit x86 software poorly; in 2003 only about 19,000 Itanium servers were sold against 4.67 million x86 servers, according to IDC analyst Mark Melanovsky.
In April 2003 AMD launched the AMD64 platform with its Opteron server chip: it extended the widely supported x86 instruction set with 64-bit registers and instructions, so one chip ran existing 32-bit applications quickly and new 64-bit ones when ready. IBM, Microsoft, Red Hat and Oracle backed it at launch.
Around 35,000 Opteron servers shipped in 2003, nearly double Itanium's count. By February 2004 Intel was shipping Xeon processors with x86-64-compatible extensions, effectively conceding that AMD's design, not Itanium, was the 64-bit standard.
Why it worked
- Existing 32-bit software ran unchanged, removing the upgrade barrier.
- Itanium's poor compatibility left buyers waiting for 64-bit apps.
- An open, published extension could be implemented by anyone, even Intel.
- Compatibility preserved skills, tools and cost from the x86 era.
What can be applied
A backward-compatible extension can beat a cleaner redesign: incumbents trade architectural purity for running today's software unchanged, and the compatible option inherits the installed base.
Aftermath
Intel adopted AMD's instruction set as EM64T, and every mainstream x86 processor since — Intel, AMD and Apple's chips — implements x86-64. Itanium was quietly discontinued, and x86-64 became the dominant 64-bit architecture in servers, PCs and the cloud.
Sources
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