Editing X86 (section)

==History==
===Designers and manufacturers===
[[File:Am386SXL-25cropped.jpg|thumb|[[Am386]], released by AMD in 1991]]
{{Further|List of former IA-32 compatible processor manufacturers}}

At various times, companies such as [[IBM]], [[VIA Technologies|VIA]], [[NEC]],{{Efn|The NEC V20 and V30 also provided the older 8080 instruction set, allowing PCs equipped with these microprocessors to operate CP/M applications at full speed (i.e., without the need to simulate an 8080 by software).}} [[AMD]], [[Texas Instruments|TI]], [[STMicroelectronics|STM]], [[Fujitsu]], [[Oki Electric Industry|OKI]], [[Siemens]], [[Cyrix]], [[Intersil]], [[Chips and Technologies|C&T]], [[NexGen]], [[United Microelectronics Corporation|UMC]], and [[Vortex86|DM&P]] started to design or manufacture{{Efn|[[Fabless]] companies designed the chip and contracted another company to manufacture it, while fabbed companies would do both the design and the manufacturing themselves. Some companies started as fabbed manufacturers and later became fabless designers, one such example being AMD.}} x86 [[central processing unit|processors]] (CPUs) intended for personal computers and embedded systems. Other companies that designed or manufactured x86 or [[x87]] processors include [[ITT Corporation]], [[National Semiconductor]], ULSI System Technology, and [[Weitek]].

Such x86 implementations were seldom simple copies but often employed different internal [[microarchitecture]]s and different solutions at the electronic and physical levels. Quite naturally, early compatible microprocessors were 16-bit, while 32-bit designs were developed much later. For the [[personal computer]] market, real quantities started to appear around 1990 with [[i386]] and [[i486]] compatible processors, often named similarly to Intel's original chips. 

After the fully [[Instruction pipelining|pipelined]] [[i486]], in 1993 [[Intel]] introduced the [[Pentium]] brand name (which, unlike numbers, could be [[trademark]]ed) for their new set of [[superscalar]] x86 designs. With the x86 naming scheme now legally cleared, other x86 vendors had to choose different names for their x86-compatible products, and initially some chose to continue with variations of the numbering scheme: [[IBM]] partnered with [[Cyrix]] to produce the [[Cyrix Cx5x86|5x86]] and then the very efficient [[6x86]] (M1) and [[6x86]]MX ([[Cyrix 6x86|MII]]) lines of Cyrix designs, which were the first x86 microprocessors implementing [[register renaming]] to enable [[speculative execution]].

AMD meanwhile designed and manufactured the advanced but delayed [[5k86]] ([[AMD K5|K5]]), which, internally, was closely based on AMD's earlier [[29K]] [[RISC]] design; similar to [[NexGen]]'s [[Nx586]], it used a strategy such that dedicated pipeline stages decode x86 instructions into uniform and easily handled [[micro-operation]]s, a method that has remained the basis for most x86 designs to this day.

Some early versions of these microprocessors had heat dissipation problems. The 6x86 was also affected by a few minor compatibility problems, the [[Nx586]] lacked a [[floating-point unit]] (FPU) and (the then crucial) pin-compatibility, while the [[AMD K5|K5]] had somewhat disappointing performance when it was (eventually) introduced.

Customer ignorance of alternatives to the Pentium series further contributed to these designs being comparatively unsuccessful, despite the fact that the [[AMD K5|K5]] had very good Pentium compatibility and the [[6x86]] was significantly faster than the Pentium on integer code.{{Efn|It had a slower FPU however, which is slightly ironic as Cyrix started out as a designer of fast floating-point units for x86 processors.}} [[AMD]] later managed to grow into a serious contender with the [[AMD K6|K6]] set of processors, which gave way to the very successful [[Athlon]] and [[Opteron]].

There were also other contenders, such as [[Centaur Technology]] (formerly [[Integrated Device Technology|IDT]]), [[Rise Technology]], and [[Transmeta]]. [[VIA Technologies]]' energy efficient [[VIA C3|C3]] and [[VIA C7|C7]] processors, which were designed by the [[Centaur Technology|Centaur]] company, were sold for many years following their release in 2005. Centaur's 2008 design, the [[VIA Nano]], was their first processor with [[superscalar]] and [[speculative execution]]. It was introduced at about the same time (in 2008) as Intel introduced the [[Intel Atom]], its first "in-order" processor after the [[P5 (microarchitecture)|P5]] [[Pentium]].

Many additions and extensions have been added to the original x86 instruction set over the years, almost consistently with full [[backward compatibility]].{{Efn|Intel abandoned its "x86" naming scheme with the ''[[P5 (microarchitecture)|P5]] [[Pentium]]'' during 1993 (as numbers could not be trademarked). However, the term x86 was already established among technicians, compiler writers etc.}} The architecture family has been implemented in processors from Intel, [[Cyrix]], [[AMD]], [[VIA Technologies]] and many other companies; there are also open implementations, such as the Zet SoC platform (currently inactive).<ref>{{cite web |date=November 4, 2013 |title=Zet: The x86 (IA-32) open implementation: Overview |url=http://opencores.org/project,zet86 |url-status=live |archive-url=https://web.archive.org/web/20180211072830/https://opencores.org/project,zet86 |archive-date=February 11, 2018 |access-date=January 5, 2014 |website=OpenCores}}</ref> Nevertheless, of those, only Intel, AMD, VIA Technologies, and [[Vortex86|DM&P Electronics]] hold x86 architectural licenses, and from these, only the first two actively produce modern 64-bit designs, leading to what has been called a "duopoly" of Intel and AMD in x86 processors.

However, in 2014 the Shanghai-based Chinese company [[Zhaoxin]], a joint venture between a Chinese company and VIA Technologies, began designing VIA based x86 processors for desktops and laptops. The release of its newest "7" family<ref>{{Cite web |title=Zhaoxin Preparing Linux Kernel Support For 7-Series Centaur CPUs |url=https://www.phoronix.com/scan.php?page=news_item&px=Zhaoxin-Centaur-Family-7-Bits |access-date=2022-04-05 |website=www.phoronix.com |language=en}}</ref> of x86 processors (e.g. KX-7000), which are not quite as fast as AMD or Intel chips but are still state of the art,<ref>{{Cite web |title=Zhaoxin aiming at 2021 release for its 7nm x86 CPUs - CPU - News - HEXUS.net |url=https://m.hexus.net/tech/news/cpu/137873-zhaoxin-aiming-2021-release-7nm-x86-cpus/ |access-date=2022-04-05 |website=m.hexus.net}}</ref> had been planned for 2021; as of March 2022 the release had not taken place, however.<ref>{{Cite web |title=Zhaoxin Finally Adding "Lujiazui" x86_64 CPU Tuning To GCC |url=https://www.phoronix.com/scan.php?page=news_item&px=Zhaoxin-lujiazui-GCC |access-date=2022-04-05 |website=www.phoronix.com |language=en}}</ref>

===From 16-bit and 32-bit to 64-bit architecture===
The [[instruction set architecture]] has twice been extended to a larger [[Word (computer architecture)|word]] size. In 1985, Intel released the 32-bit 80386 (later known as i386) which gradually replaced the earlier 16-bit chips in computers (although typically not in [[embedded system]]s) during the following years; this extended programming model was originally referred to as ''the i386 architecture'' (like its first implementation) but Intel later dubbed it [[IA-32]] when introducing its (unrelated) [[IA-64]] architecture.

In 1999–2003, [[Advanced Micro Devices|AMD]] extended this 32-bit architecture to 64&nbsp;bits and referred to it as [[x86-64]] in early documents and later as [[AMD64]]. Intel soon adopted AMD's architectural extensions under the name IA-32e, later using the name EM64T and finally using Intel 64. [[Microsoft]] and [[Sun Microsystems]]/[[Oracle Corporation|Oracle]] also use term "x64", while many [[Linux distribution]]s, and the [[BSD]]s also use the "amd64" term. Microsoft Windows, for example, designates its 32-bit versions as "x86" and 64-bit versions as "x64", while installation files of 64-bit Windows versions are required to be placed into a directory called "AMD64".<ref>{{cite web|url=http://support.microsoft.com/kb/896334|title=Setup and installation considerations for Windows x64 Edition-based computers|access-date=September 14, 2014|archive-date=September 11, 2014|archive-url=https://web.archive.org/web/20140911011914/http://support.microsoft.com/kb/896334|url-status=live}}</ref>

In 2023, Intel proposed a major change to the architecture referred to as [[X86-64#X86S|X86S]] (formerly known as X86-S). The S in X86S stood for "simplification", which aimed to remove support for legacy execution modes and instructions. A processor implementing this proposal would start execution directly in [[long mode]] and would only support 64-bit operating systems. 32-bit code would only be supported for user applications running in ring 3, and would use the same simplified segmentation as long mode.<ref>{{Cite web |title=Envisioning a Simplified Intel Architecture |url=https://www.intel.com/content/www/us/en/developer/articles/technical/envisioning-future-simplified-architecture.html |website=Intel}}</ref><ref>{{Cite news |last=Larabel |first=Michael |date=2023-05-20 |title=Intel Publishes "X86-S" Specification For 64-bit Only Architecture |work=[[Phoronix]] |url=https://www.phoronix.com/news/Intel-X86-S-64-bit-Only |access-date=2023-05-20}}</ref> In December 2024 Intel cancelled this project.<ref>{{Cite web |title=toms hardware X86S |url=https://www.tomshardware.com/pc-components/cpus/intel-terminates-x86s-initiative-unilateral-quest-to-de-bloat-x86-instruction-set-comes-to-an-end}}</ref>