x86-64

x86-64 (also known as x64, x86_64, AMD64, and Intel 64) is a <a href="/facts/64-bit/AgvkQHkM">64-bit</a> extension of the <a href="/facts/X86/Kypq5fgu">x86</a> <a href="/facts/Instruction_set_architecture/8p8vwUeE">instruction set.</a> It was announced in 1999 and first available in the <a href="/facts/AMD_Opteron/IF1ueyIJ">AMD Opteron</a> family in 2003. It introduces two new operating modes: 64-bit mode and compatibility mode, along with a new four-level <a href="/facts/Paging/KR889x5k">paging</a> mechanism.
In 64-bit mode, x86-64 supports significantly larger amounts of <a href="/facts/Virtual_memory/Lw2GemF5">virtual memory</a> and <a href="/facts/Physical_memory/wPHKFpdx">physical memory</a> compared to its <a href="/facts/32-bit_computing/TDMVce8s">32-bit</a> predecessors, allowing programs to utilize more memory for data storage. The architecture expands the number of <a href="/facts/General-purpose_register/32RvbUdz">general-purpose registers</a> from 8 to 16, all fully general-purpose, and extends their width to 64 bits.
<a href="/facts/Floating-point_arithmetic/eIckahxe">Floating-point arithmetic</a> is supported through mandatory <a href="/facts/SSE2/cheNDPSK">SSE2</a> instructions in 64-bit mode. While the older <a href="/facts/X87/y8X9HnLL">x87</a> FPU and MMX registers are still available, they are generally superseded by a set of sixteen 128-bit <a href="/facts/Processor_register/32RvbUdz">vector registers</a> (XMM registers). Each of these vector registers can store one or two <a href="/facts/Double-precision_floating-point_format/JYyXXYFM">double-precision floating-point numbers</a>, up to four <a href="/facts/Single-precision_floating-point_format/e6Fez7BM">single-precision</a> floating-point numbers, or various integer formats.
In 64-bit mode, instructions are modified to support 64-bit <a href="/facts/Operands/HSuUzrKz">operands</a> and 64-bit <a href="/facts/Addressing_mode/g78wINgK">addressing mode</a>.
The x86-64 architecture defines a compatibility mode that allows 16-bit and 32-bit <a href="/facts/User_space/0yIzMY8t">user applications</a> to run unmodified alongside 64-bit applications, provided the 64-bit operating system supports them. Since the full x86-32 instruction sets remain implemented in hardware without the need for emulation, these older <a href="/facts/Executable/VSst9eLA">executables</a> can run with little or no performance penalty, while newer or modified applications can take advantage of new features of the processor design to achieve performance improvements. Also, processors supporting x86-64 still power on in <a href="/facts/Real_mode/wfU8vfjn">real mode</a> to maintain <a href="/facts/Backward_compatibility/FbHFBu5y">backward compatibility</a> with the original <a href="/facts/Intel_8086/sS9dlSdK">8086 processor</a>, as has been the case with x86 processors since the introduction of <a href="/facts/Protected_mode/y5u3Gwqq">protected mode</a> with the <a href="/facts/Intel_80286/rucEU93g">80286</a>.
The original specification, created by <a href="/facts/AMD/CB1G7QTb">AMD</a> and released in 2000, has been implemented by AMD, <a href="/facts/Intel_Corporation/SMF0gJJX">Intel</a>, and <a href="/facts/VIA_Technologies/g6REHNFE">VIA</a>. The <a href="/facts/AMD_K8/31Fh4soT">AMD K8</a> <a href="/facts/Microarchitecture/NFRd4NUL">microarchitecture</a>, in the <a href="/facts/Opteron/IF1ueyIJ">Opteron</a> and <a href="/facts/Athlon_64/3JLpVnQd">Athlon 64</a> processors, was the first to implement it. This was the first significant addition to the <a href="/facts/X86/Kypq5fgu">x86</a> architecture designed by a company other than Intel. Intel was forced to follow suit and introduced a modified <a href="/facts/NetBurst/QIkVG48W">NetBurst</a> family which was software-compatible with AMD's specification. <a href="/facts/VIA_Technologies/g6REHNFE">VIA Technologies</a> introduced x86-64 in their VIA Isaiah architecture, with the <a href="/facts/VIA_Nano/82nYJeBy">VIA Nano</a>.
The x86-64 architecture was quickly adopted for desktop and laptop personal computers and servers which were commonly configured for 16 GiB (<a href="/facts/Gibibyte/BNHUp9Qq">gibibytes</a>) of memory or more. It has effectively replaced the discontinued Intel <a href="/facts/Itanium/0wkjSDpe">Itanium</a> architecture (formerly <a href="/facts/IA-64/m6egpGno">IA-64</a>), which was originally intended to replace the x86 architecture. x86-64 and Itanium are not compatible on the native instruction set level, and operating systems and applications compiled for one architecture cannot be run on the other natively.

x86-64 open-in-new

x86-64