About X86

X86. Generic denomination given to certain Microprocessors of the Intel family, their compatible ones and the basic architecture to which these processors belong, by the ending of their numerical names: 8086, 80286, 80386, 80486, etc. According to abbreviationfinder, they have been a standard for computers of the IBM PC Compatible type since their birth . They are commonly known by shortened versions of their names, such as 286 or I286, 386 or I386, 486 or I486, and even 086, for I8086 or I8088 (their respective 8-bit version). The commercial popularity of this architecture caused many manufacturers, in addition to Intel, to begin mass-producing microprocessors based on this architecture. These companies include AMD, Cyrix, NEC Corporation and Transmeta, among others.


The architecture known as x86 begins in 1978 with the Intel 8086/88 processors (although the 4004, 8080, and 8085 had previously appeared .). These processors belonged to the IA-16 architecture (Intel Architecture 16 bits).

Throughout its evolution, since 1978, Intel has maintained binary compatibility with preceding processors. This compatibility breaks with the Itanium and Itanium2 processors, with IA-64 architecture, which are totally incompatible with their predecessors.

The (80)386 was Intel’s first processor with a 32-bit instruction set (IA-32). Both the operands and the addressing in memory use 32 bits, so the 386 has a 4GB address space.

The 386 is also the first to introduce a paging MMU, with a fixed page size of 4KB. Previous processors already had a segmentation scheme, which in the 386 can be bypassed by using a flat memory scheme.

Some processors with x86 architecture

intel processors

  • 80486DX2 and an Intel 80386.
  • Intel Pentium.
  • Intel PentiumII.
  • Intel PentiumIII.
  • Intel Pentium 4.

AMD processors

  • AMD Athlon.
  • AMD Athlon 64.
  • AthlonXP.
  • AMD Duron.
  • AMD Opteron.
  • AMD Sempron.

Operating modes

  • Protected mode: It is the normal operating mode of the processor, in which all its features are available.
  • Real-addressing mode: This is a compatibility mode with the 8086, except for the ability to switch to protected mode. The processor always starts its execution in this mode (after boot or reset).
  • Maintenance mode: It is a mode entered by an APIC interrupt, useful only for operating system maintenance tasks (management of power control or security).

Basic characteristics

  • The x86 architecture is a variable instruction length, memory register type, and CISC design.
  • Linear address space is 4GB, although physical memory can go up to 64GB on some models, with unaligned access and Little-endian storage.
  • A typical program has 8 32-bit general purpose registers, 6 16-bit segment registers, an EFLAGS status register, and an EIP instruction pointer, both 32-bit. These registers can be accessed from general purpose operations, made up of integer arithmetic instructions, flow control instructions, bit and byte string operations, and memory access instructions.
  • A set of 8 80-bit floating point registers, a set of 8 MMX and XMM registers, 64 and 128 bits respectively, to perform SIMD operations.
  • A set of resources for stack handling and subroutine invocation.
  • The OS also has I/O ports, control registers, memory management, debugging, monitoring, etc.