AMD64

x86-64 (also known as x64, x86_64 and AMD64) is the 64-bit version of the x86 instruction set. It supports vastly larger amounts (theoretically, 2⁶⁴ bytes or 16 exabytes) of virtual memory and physical memory than is possible on its 32-bit predecessors, allowing programs to store larger amounts of data in memory. x86-64 also provides 64-bit general-purpose registers and numerous other enhancements. It is fully backward compatible with 16-bit and 32-bit x86 code. Because the full x86 16-bit and 32-bit instruction sets remain implemented in hardware without any intervening emulation, existing x86 executables run with no compatibility or performance penalties, whereas existing applications that are recoded to take advantage of new features of the processor design may achieve performance improvements.

The original specification, created by AMD and released in 2000, has been implemented by AMD, Intel and VIA. The AMD K8 processor was the first to implement the architecture; this was the first significant addition to the x86 architecture designed by a company other than Intel. Intel was forced to follow suit and introduced a modified NetBurst family which was fully software-compatible with AMD's design and specification. VIA Technologies introduced x86-64 in their VIA Isaiah architecture, with the VIA Nano.

The x86-64 specification is distinct from the Intel Itanium (formerly IA-64) architecture, which is not compatible on the native instruction set level with the x86 architecture.

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