View source for IA-32

{{Short description|32-bit version of x86 architecture}}

'''IA-32''' (short for "'''Intel Architecture, 32-bit'''", commonly called ''i386''<ref name="Ditto" /><ref name="Intelli" />)<ref name="Adm" /> is the [[32-bit|32-bit]] version of the [[X86|x86]] [[Instruction set architecture|instruction set architecture]], designed by [[Company:Intel|Intel]] and first implemented in the [[Engineering:I386|80386]] [[Engineering:Microprocessor|microprocessor]] in 1985.  IA-32 is the first incarnation of x86 that supports 32-bit computing;<ref>{{Cite web
  |url = http://www.intel.com/content/www/us/en/processors/architectures-software-developer-manuals.html
  |title = Intel 64 and IA-32 Architectures Software Developer's Manual
  |publisher = Intel Corporation
  |page = 31
  |date = September 2014
  |quote = The Intel386 processor was the first 32-bit processor in the IA-32 architecture family. It introduced 32-bit registers for use both to hold operands and for addressing.
  |access-date = December 19, 2014
  |archive-date = January 26, 2012
  |archive-url = https://web.archive.org/web/20120126002939/http://www.intel.com/content/www/us/en/processors/architectures-software-developer-manuals.html
  |url-status = live
  }}</ref> as a result, the "IA-32" term may be used as a metonym to refer to all x86 versions that support 32-bit computing.<ref name="Generally so" /><ref name="Generally So - Ubuntu" />

Within various [[Programming language|programming language]] directives, IA-32 is still sometimes referred to as the "i386" architecture. In some other contexts, certain iterations of the IA-32 ISA are sometimes labelled ''i486'', ''i586'' and ''i686'', referring to the instruction supersets offered by the [[Engineering:I486|80486]], the [[Engineering:P5 (microarchitecture)|P5]] and the [[Engineering:P6 (microarchitecture)|P6 microarchitectures]] respectively. These updates offered numerous additions alongside the base IA-32 set including [[X87|floating-point capabilities]] and the [[MMX (instruction set)|MMX extensions]].

Intel was historically the largest manufacturer of IA-32 processors, with the second biggest supplier having been [[Company:Advanced Micro Devices|AMD]]. During the 1990s, [[Company:VIA Technologies|VIA]], [[Company:Transmeta|Transmeta]] and other chip manufacturers also produced IA-32 compatible processors (e.g. WinChip). In the modern era, Intel still produced IA-32 processors under the [[Engineering:Intel Quark|Intel Quark]] [[Engineering:Microcontroller|microcontroller]] platform until 2019; however, since the 2000s, the majority of manufacturers (Intel included) moved almost exclusively to implementing CPUs based on the 64-bit variant of x86, [[X86-64|x86-64]]. x86-64, by specification, offers legacy operating modes that operate on the IA-32 ISA for backwards compatibility. Even given the contemporary prevalence of x86-64, {{as of|2023|lc=true}}, IA-32 protected mode versions of many modern operating systems are still maintained, e.g. [[Software:Microsoft Windows|Microsoft Windows]] (until [[Software:Windows 10|Windows 10]]; [[Software:Windows 11|Windows 11]] requires [[X86-64|x86-64]]-compatible processor for x86 versions),<ref>{{Cite web|url=https://www.microsoft.com/en-us/windows/windows-10-specifications#primaryR2|title=Windows 10 System Requirements & Specifications {{!}} Microsoft|website=www.microsoft.com|language=en-us|access-date=August 20, 2018|archive-date=May 1, 2018|archive-url=https://web.archive.org/web/20180501190351/https://www.microsoft.com/en-us/windows/windows-10-specifications#primaryR2|url-status=live}}</ref> Windows Server (until [[Software:Windows Server 2008|Windows Server 2008]]; [[Software:Windows Server 2008 R2|Windows Server 2008 R2]] requires [[X86-64|x86-64]]-compatible processor for x86 versions)<ref>{{Cite web|url=https://betanews.com/2007/05/16/windows-server-2008-the-last-32-bit-operating-system/|title=Windows Server 2008 'The Last 32-bit Operating System'|author=Scott M. Fulton, III|website=BetaNews|date=May 16, 2007 }}</ref> and the [[Software:Debian|Debian]] [[Software:Linux|Linux]] distribution.<ref>{{Cite web|url=https://www.debian.org/ports/i386/|title=Debian GNU/Linux on x86 Machines|access-date=August 20, 2020|archive-date=April 28, 2019|archive-url=https://web.archive.org/web/20190428051247/https://www.debian.org/ports/i386/|url-status=live}}</ref> In spite of IA-32's name (and causing some potential confusion), the 64-bit evolution of x86 that originated out of AMD would not be known as "IA-64", that name instead belonging to [[Engineering:IA-64|Intel's Itanium architecture]].

== Architectural features ==

The primary defining characteristic of IA-32 is the availability of 32-bit general-purpose [[Processor register|processor register]]s (for example, EAX and EBX), 32-bit [[Integer (computer science)|integer]] arithmetic and logical operations, 32-bit offsets within a segment in [[Protected mode|protected mode]], and the translation of segmented addresses to 32-bit linear addresses. The designers took the opportunity to make other improvements as well. Some of the most significant changes (relative to the 16-bit [[Engineering:Intel 80286|286]] instruction set) are:

; 32-bit integer capability: All general-purpose registers (GPRs) are expanded from 16&nbsp;[[Bit|bit]]s to 32&nbsp;bits, and all arithmetic and logical operations, memory-to-register and register-to-memory operations, etc., can operate directly on 32-bit integers. Pushes and pops on the [[Stack register|stack]] default to 4-byte strides, and non-segmented [[Pointer (computer programming)|pointers]] are 4 bytes wide.
; More general addressing modes: Any GPR can be used as a base register, and any GPR other than ESP can be used as an index register, in a memory reference.  The index register value can be multiplied by 1, 2, 4, or 8 before being added to the base register value and displacement.
; Additional segment registers: Two additional segment registers, FS and GS, are provided.
; Larger virtual address space: The IA-32 architecture defines a 48-bit segmented address format, with a 16-bit segment number and a 32-bit offset within the segment.  Segmented addresses are mapped to 32-bit linear addresses.
; Demand paging: 32-bit linear addresses are virtual addresses rather than physical addresses; they are translated to physical addresses through a [[Page table|page table]].  In the 80386, 80486, and the [[Engineering:P5 (microarchitecture)|original Pentium]] processors, the physical address was 32 bits; in the [[Engineering:Pentium Pro|Pentium Pro]] and later processors, the [[Physical Address Extension]] allowed 36-bit physical addresses, although the linear address size was still 32 bits.

== Operating modes ==
{| class="wikitable"
|-
! Operating mode
! [[Operating system]] required
! Type of code being run
! Default address size
! Default operand size
! Typical GPR width
|-
| rowspan="2" | [[Protected mode]]
| 32-bit operating system or boot loader
| 32-bit protected-mode code
| 32 bits
| 32 bits
| 32 bits
|-
| 16-bit protected-mode operating system or boot loader, or 32-bit boot loader
| 16-bit protected-mode code
| 16 bits
| 16 bits
| 16 or 32 bits
|-
| [[Virtual 8086 mode]]
| 16- or 32-bit protected-mode operating system
| 16-bit real-mode code
| 16 bits
| 16 bits
| 16 or 32 bits
|-
| [[Real mode]]
| 16-bit real-mode operating system or boot loader, or 32-bit boot loader
| 16-bit real-mode code
| 16 bits
| 16 bits
| 16 or 32 bits
|-
| [[Unreal mode]]
| 16-bit real-mode operating system or boot loader, or 32-bit boot loader
| 16-bit real-mode code
| 32 bits
| 16 bits
| 16 or 32 bits
|}

== See also ==

* [[X86-64|x86-64]]
* [[Engineering:IA-64|IA-64]]
* [[Company:List of former IA-32 compatible processor manufacturers|List of former IA-32 compatible processor manufacturers]]
* [[Transient execution CPU vulnerability]]

==References==
{{Reflist|30em|refs=

<ref name=Intelli>{{cite web|title=Additional Predefined Macros|url=https://software.intel.com/content/www/us/en/develop/documentation/cpp-compiler-developer-guide-and-reference/top/compiler-reference/macros/additional-predefined-macros.html|work=software.intel.com|publisher=[[Company:Intel|Intel]]|access-date=November 25, 2020|archive-date=February 15, 2021|archive-url=https://web.archive.org/web/20210215084323/https://software.intel.com/content/www/us/en/develop/documentation/cpp-compiler-developer-guide-and-reference/top/compiler-reference/macros/additional-predefined-macros.html|url-status=live}}</ref> 
<ref name=Ditto>{{cite web|title=ditto(1) Mac OS X Manual Page|url=https://developer.apple.com/library/mac/#documentation/Darwin/Reference/ManPages/man1/ditto.1.html|work=BSD General Commands Manual|publisher=[[Company:Apple Inc.|Apple]]|access-date=August 3, 2013|date=December 19, 2008|quote=Thin Universal binaries to the specified architecture [...] should be specified as "i386", "x86_64", etc.|archive-date=June 2, 2012|archive-url=https://web.archive.org/web/20120602013413/https://developer.apple.com/library/mac/#documentation/Darwin/Reference/ManPages/man1/ditto.1.html|url-status=dead}}</ref>

<ref name=Adm>{{cite web|last=Kemp|first=Steve|title=Running 32-bit Applications on 64-bit Debian GNU/Linux|url=http://www.debian-administration.org/articles/534|work=Debian Administration|access-date=August 31, 2013|archive-date=September 16, 2013|archive-url=https://web.archive.org/web/20130916160905/http://www.debian-administration.org/articles/534|url-status=dead}}</ref>

<ref name="Generally so">{{cite web |first=Ronald W. |last=Green |title=What do IA-32, Intel 64 and IA-64 Architecture mean? |url=https://software.intel.com/en-us/articles/ia-32-intelr-64-ia-64-architecture-mean/ |website=software.intel.com |publisher=[[Company:Intel|Intel]] |date=May 5, 2009 |access-date=December 19, 2014 |archive-date=December 19, 2014 |archive-url=https://web.archive.org/web/20141219144304/https://software.intel.com/en-us/articles/ia-32-intelr-64-ia-64-architecture-mean/ |url-status=live }}</ref>

<ref name="Generally So - Ubuntu">{{cite web|title=Supported Hardware|url=https://help.ubuntu.com/12.04/installation-guide/en.i386/ch02s01.html|archive-url=https://archive.today/20141219153039/https://help.ubuntu.com/12.04/installation-guide/en.i386/ch02s01.html|url-status=dead|archive-date=December 19, 2014|work=Ubuntu Help|publisher=Canonical|access-date=August 31, 2013}}</ref>

}}

[[Category:X86 architecture]]

{{Sourceattribution|IA-32}}