Who created the x86-64 (AMD64) architecture, and why did it win over Intel's Itanium?
AMD created x86-64 (AMD64) in 2003 as an evolutionary 64-bit extension of x86; it won because, unlike Intel's clean-slate Itanium, it ran existing 32-bit software natively.
The two companies bet on opposite strategies for going 64-bit. Intel, with HP, designed Itanium (IA-64) — a radically new instruction set aimed at high performance that could only run old IA-32 code through a slow legacy mode. AMD instead simply extended x86 to 64 bits, keeping full backwards compatibility. With billions of lines of x86 software in existence, that compatibility was decisive: Itanium would have required rewrites, its compilers couldn't match hand-tuned x86, and the Pentium 4 line got "too good." The market chose AMD64, and in 2004 Intel was obliged to adopt an almost-identical extension it called EM64T.
Names for the same thing:
- AMD64 — AMD's name
- x86-64 — the neutral technical name
- x64 — Microsoft's name
- Intel 64 / EM64T — Intel's name after adopting it
The lesson recurs in computing: backwards compatibility often beats a technically cleaner but incompatible design.
Go deeper:
x86-64 (Wikipedia) — AMD's evolutionary 64-bit extension and its win over IA-64.- Itanium (Wikipedia) — the Itanium side of the story — why the clean-slate IA-64 lost.