x86-64
Processors · 5 specs
Direct Answer
x86-64 is the 64-bit extension of the x86 architecture, developed by AMD and first specified in 1999-2000 under the name AMD64, shipping in the 2003 Opteron. Intel followed with its own compatible implementation in 2004, initially branded EM64T and renamed Intel 64 in 2006.
Source: AMD (original specification, 1999-2000) · Last reviewed Aug 28, 2026
Specs
| Developer | AMD (original specification) |
| Announced / Full Spec | 1999 / August 2000 |
| First Processor | AMD Opteron, April 2003 |
| Intel's Version | EM64T (March 2004), renamed Intel 64 (2006) |
| Backward Compatible | Yes, with 32-bit and 16-bit x86 code |
AMD Wrote the Spec, Intel Followed It
AMD announced its 64-bit x86 extension, branded AMD64, in 1999, with a full specification published in August 2000; the first processor implementing it, the Opteron, shipped in April 2003. Intel had been pursuing its own, incompatible 64-bit architecture at the time (IA-64, used in Itanium), but ultimately adopted AMD's approach instead -- Intel's compatible implementation launched in June 2004 under the name EM64T (Extended Memory 64 Technology), and was renamed Intel 64 in late 2006. Both companies' chips implement the same underlying x86-64 instruction set, which is why the architecture is generally referred to by that neutral name rather than either company's original branding today.
x86-64 defines a compatibility mode that lets 32-bit and 16-bit x86 applications run unmodified alongside 64-bit software, which smoothed the industry's transition away from pure 32-bit computing. It remains the dominant architecture for desktop, laptop, and server computing.