Editing X86 (section)

===x86-64===
{{More citations needed section|date=March 2016}}
{{Main|x86-64}}

[[File:Processor families in TOP500 supercomputers.svg|thumb|upright=1.25|In [[supercomputer]] [[computer cluster|cluster]]s (as tracked by [[TOP 500]] data and visualized on the diagram above, last updated 2013), the appearance of 64-bit extensions for the x86 architecture enabled 64-bit x86 processors by AMD and Intel (teal hatched and blue hatched, in the diagram, respectively) to replace most RISC processor architectures previously used in such systems (including [[PA-RISC]], [[SPARC]], [[DEC Alpha|Alpha]], and others), and 32-bit x86 (green on the diagram), even though Intel initially tried unsuccessfully to replace x86 with a new incompatible 64-bit architecture in the [[Itanium]] processor. The main non-x86 architecture which is still used, as of 2014, in supercomputing clusters is the [[Power ISA]] used by [[IBM Power microprocessors]] (blue with diamond tiling in the diagram), with SPARC as a distant second.]]

By the 2000s, 32-bit x86 processors' limits in memory addressing were an obstacle to their use in high-performance computing clusters and powerful desktop workstations. The aged 32-bit x86 was competing with much more advanced 64-bit RISC architectures which could address much more memory. Intel and the whole x86 ecosystem needed 64-bit memory addressing if x86 was to survive the 64-bit computing era, as workstation and desktop software applications were soon to start hitting the limits of 32-bit memory addressing. However, Intel felt that it was the right time to make a bold step and use the transition to 64-bit desktop computers for a transition away from the x86 architecture in general, an experiment which ultimately failed.

In 2001, Intel attempted to introduce a non-x86 64-bit architecture named [[IA-64]] in its [[Itanium]] processor, initially aiming for the [[high-performance computing]] market, hoping that it would eventually replace the 32-bit x86.<ref>{{cite web
 |url          = http://features.techworld.com/operating-systems/2690/will-intel-abandon-the-itanium/
 |title        = Will Intel abandon the Itanium?
 |date         = July 20, 2006
 |author       = Manek Dubash
 |quote        = Once touted by Intel as a replacement for the x86 product line, expectations for Itanium have been throttled well back.
 |publisher    = [[Techworld]]
 |access-date  = December 19, 2010
 |archive-date = February 19, 2011
 |archive-url  = https://web.archive.org/web/20110219212053/http://features.techworld.com/operating-systems/2690/will-intel-abandon-the-itanium/
 |url-status   = dead
}}</ref> While IA-64 was incompatible with x86, the Itanium processor did provide [[Emulator|emulation]] abilities for translating x86 instructions into IA-64, but this affected the performance of x86 programs so badly that it was rarely, if ever, actually useful to the users: programmers should rewrite x86 programs for the IA-64 architecture or their performance on Itanium would be orders of magnitude worse than on a true x86 processor. The market rejected the Itanium processor since it broke [[backward compatibility]] and preferred to continue using x86 chips, and very few programs were rewritten for IA-64.

AMD decided to take another path toward 64-bit memory addressing, making sure backward compatibility would not suffer. In April 2003, AMD released the first x86 processor with 64-bit general-purpose registers, the [[Opteron]], capable of addressing much more than 4&nbsp;[[Gigabyte|GB]] of virtual memory using the new [[x86-64]] extension (also known as AMD64 or x64). The 64-bit extensions to the x86 architecture were enabled only in the newly introduced [[long mode]], therefore 32-bit and 16-bit applications and operating systems could simply continue using an AMD64 processor in protected or other modes, without even the slightest sacrifice of performance<ref name="x86-compat-perf">{{cite web
  |url=https://public.dhe.ibm.com/software/webserver/appserv/was/64bitPerf.pdf
  |title=IBM WebSphere Application Server 64-bit Performance Demystified
  |page=14
  |quote=Figures 5, 6 and 7 also show the 32-bit version of WAS runs applications at full native hardware performance on the POWER and x86-64 platforms. Unlike some 64-bit processor architectures, the POWER and x86-64 hardware does not emulate 32-bit mode. Therefore applications that do not benefit from 64-bit features can run with full performance on the 32-bit version of WebSphere running on the above mentioned 64-bit platforms.
  |publisher=IBM Corporation
  |date=September 6, 2007
  |access-date=April 9, 2010
  |archive-date=January 25, 2022
  |archive-url=https://web.archive.org/web/20220125121650/ftp://ftp.software.ibm.com/software/webserver/appserv/was/64bitPerf.pdf
  |url-status=live
  }}</ref> and with full compatibility back to the original instructions of the 16-bit Intel 8086.<ref name="amd-24593">{{cite web
  |url=https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/programmer-references/24593.pdf
  |title=Volume 2: System Programming
  |date=March 2024
  |work=AMD64 Architecture Programmer's Manual
  |publisher=AMD Corporation
  |access-date=April 24, 2024
  |archive-date=April 4, 2024
  |archive-url=https://web.archive.org/web/20240404110900/https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/programmer-references/24593.pdf
  |url-status=live
  }}</ref>{{rp|page=13–14|date=November 2012}} The market responded positively, adopting the 64-bit AMD processors for both high-performance applications and business or home computers.

Seeing the market rejecting the incompatible Itanium processor and Microsoft supporting AMD64, Intel had to respond and introduced its own x86-64 processor, the ''[[Pentium 4#Prescott|Prescott]]'' Pentium&nbsp;4, in July 2004.<ref>{{cite news
  |author= Charlie Demerjian
  |title=Why Intel's Prescott will use AMD64 extensions
  |url=http://www.theinquirer.net/inquirer/news/1029651/why-intels-prescott-will-use-amd64--extensions
  |archive-url=https://web.archive.org/web/20091010181925/http://www.theinquirer.net/inquirer/news/1029651/why-intels-prescott-will-use-amd64--extensions
  |url-status=dead
  |archive-date=October 10, 2009
  |work=[[The Inquirer]]
  |date=September 26, 2003
  |access-date=October 7, 2009
}}</ref> As a result, the Itanium processor with its IA-64 instruction set is rarely used and x86, through its x86-64 incarnation, is still the dominant CPU architecture in non-embedded computers.

x86-64 also introduced the [[NX bit]], which offers some protection against security bugs caused by [[buffer overrun]]s.

As a result of AMD's 64-bit contribution to the x86 lineage and its subsequent acceptance by Intel, the 64-bit RISC architectures ceased to be a threat to the x86 ecosystem and almost disappeared from the workstation market. x86-64 began to be utilized in powerful [[supercomputer]]s (in its [[AMD Opteron]] and [[Intel Xeon]] incarnations), a market which was previously the natural habitat for 64-bit RISC designs (such as the [[IBM Power microprocessors]] or [[SPARC]] processors). The great leap toward 64-bit computing and the maintenance of backward compatibility with 32-bit and 16-bit software enabled the x86 architecture to become an extremely flexible platform today, with x86 chips being utilized from small low-power systems (for example, [[Intel Quark]] and [[Intel Atom]]) to fast gaming desktop computers (for example, [[Intel Core i7]] and [[AMD FX]]/[[Ryzen]]), and even dominate large supercomputing [[computer cluster|cluster]]s, effectively leaving only the [[ARM architecture|ARM]] 32-bit and 64-bit RISC architecture as a competitor in the [[smartphone]] and [[tablet computer|tablet]] market.