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x86 is a family of backward compatible instruction set architectures based on the Intel 8086 CPU and its Intel 8088 variant. The 8086 was introduced in 1978 as a fully 16-bit extension of Intel's 8-bit based 8080 microprocessor, with memory segmentation as a solution for addressing more memory than can be covered by a plain 16-bit address. The term "x86" came into being because the names of several successors to Intel's 8086 processor end in "86", including the 80186, 80286, 80386 and 80486 processors.

x86
Designer Intel, AMD
Bits 16-bit, 32-bit and 64-bit
Introduced 1978 (16-bit), 1985 (32-bit), 2003 (64-bit)
Design CISC
Type Register-memory
Encoding Variable (1 to 15 bytes)
Branching Condition code
Endianness Little
Page size 8086i286: None
i386, i486: 4 KB pages
P5 Pentium: added 4 MB pages
(Legacy PAE: 4 KB→2 MB)
x86-64: added 1 GB pages
Extensions x87, IA-32, MMX, SSE, SSE2, x86-64, SSE3, SSSE3, SSE4, SSE5, AVX
Open Partly. For some advanced features, x86 may require license from Intel; x86-64 may require an additional license from AMD. The 80486 processor has been on the market for more than 20 years and so cannot be subject to patent claims. The pre-586 subset of the x86 architecture is therefore fully open.
Registers
General purpose
  • 16-bit: six semi-dedicated registers, BP and SP are not general-purpose
  • 32-bit: eight GPRs, including EBP and ESP
  • 64-bit: 16 GPRs, including RBP and RSP
Floating point
  • 16-bit: optional separate x87 FPU
  • 32-bit: optional separate or integrated x87 FPU, integrated SSE2 units in later processors
  • 64-bit: integrated x87 and SSE2 units
Intel 8086
Intel Core 2 Duo – an example of an x86-compatible, 64-bit multicore processor
AMD Athlon (early version) – a technically different but fully compatible x86 implementation

x86 is a family of backward compatible instruction set architectures based on the Intel 8086 CPU and its Intel 8088 variant. The 8086 was introduced in 1978 as a fully 16-bit extension of Intel's 8-bit based 8080 microprocessor, with memory segmentation as a solution for addressing more memory than can be covered by a plain 16-bit address. The term "x86" came into being because the names of several successors to Intel's 8086 processor end in "86", including the 80186, 80286, 80386 and 80486 processors.

Many additions and extensions have been added to the x86 instruction set over the years, almost consistently with full backward compatibility. The architecture has been implemented in processors from Intel, Cyrix, AMD, VIA and many other companies; there are also open implementations, such as the Zet SoC platform.

The term is not synonymous with IBM PC compatibility as this implies a multitude of other computer hardware; embedded systems as well as general-purpose computers used x86 chips before the PC-compatible market started, some of them before the IBM PC (1981) itself.

As of 2016, the majority of personal computers and laptops sold are based on the x86 architecture (despite inroads from Chromebook-style ARM designs, the segment-leading Apple MacBook family remains exclusively x86), while other categories—especially high-volume mobile categories such as smartphones or tablets—are dominated by ARM; at the high end, x86 continues to dominate compute-intensive workstation and cloud computing segments.