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x86-64 (also known as x64, x86_64, AMD64, and Intel 64) [note 1] is a 64-bit extension of the x86 instruction set architecture first announced in 1999. It introduces two new operating modes: 64-bit mode and compatibility mode, along with a new four-level paging mechanism.
Computer architectures are often described as n-bit architectures. In the first 3 ⁄ 4 of the 20th century, n is often 12, 18, 24, 30, 36, 48 or 60.In the last 1 ⁄ 3 of the 20th century, n is often 8, 16, or 32, and in the 21st century, n is often 16, 32 or 64, but other sizes have been used (including 6, 39, 128).
Linux distributions refer to it either as "x86-64", its variant "x86_64", or "amd64". BSD systems use "amd64" while macOS uses "x86_64". Long mode is mostly an extension of the 32-bit instruction set, but unlike the 16–to–32-bit transition, many instructions were dropped in the 64-bit mode.
Based on the K7 but was designed around a 64-bit ISA, added an integrated memory controller, HyperTransport communication fabric, L2 cache sizes up to 1 MB (1128 KB total cache), and SSE2. Later K8 added SSE3. The K8 was the first mainstream Windows-compatible 64-bit microprocessor and was released April 22, 2003.
The term 64-bit also describes a generation of computers in which 64-bit processors are the norm. 64 bits is a word size that defines certain classes of computer architecture, buses, memory, and CPUs and, by extension, the software that runs on them. 64-bit CPUs have been used in supercomputers since the 1970s (Cray-1, 1975) and in reduced ...
reengineered P6-based microarchitecture used in Intel Core 2 and Xeon microprocessors, built on a 65 nm process, supporting x86-64 level SSE instruction and macro-op fusion and enhanced micro-op fusion with a wider front end and decoder, larger out-of-order core and renamed register, support loop stream detector and large shadow register file.
existing instructions extended to a 64 bit address size (JRCXZ) existing instructions extended to a 64 bit operand size (remaining instructions) Most instructions with a 64 bit operand size encode this using a REX.W prefix; in the absence of the REX.W prefix, the corresponding instruction with 32 bit operand size is encoded. This mechanism also ...
An x86-64 processor acts identically to an IA-32 processor when running in real mode or protected mode, which are supported modes when the processor is not in long mode.. A bit in the CPUID extended attributes field informs programs in real or protected modes if the processor can go to long mode, which allows a program to detect an x86-64 processor.