Editing IA-32 (section)

== Architectural features ==

The primary defining characteristic of IA-32 is the availability of 32-bit general-purpose [[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]], 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 [[Intel 80286|286]] instruction set) are:

; 32-bit integer capability: All [[general-purpose register]]s (GPRs) are expanded from 16&nbsp;[[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. [[Stack (data structure)|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]].  In the 80386, [[80486]], and the [[P5 (microarchitecture)|original Pentium]] processors, the physical address was 32 bits; in the [[Pentium Pro]] and later processors, the [[Physical Address Extension]] allowed 36-bit physical addresses, although the linear address size was still 32 bits.