x86 or 80×86 is the generic name of a microprocessor architecture first developed and manufactured by Intel. The x86 architecture has dominated the desktop computer, portable computer, and small server markets since the 1980s IBM PC, running primarily versions of Microsoft Windows and Unix variant operating systems. Although more modern architectures such as PowerPC have challenged the x86 as a replacement for many niches, none have so far supplanted the x86 for its core markets.

An Intel Pentium 4 chip; early Northwood build

The architecture is called x86 because the earliest processors in this family were identified by model numbers ending in the sequence “86″: the 8086, the 80186, the 80286, the 386, and the 486. Because one cannot establish trademark rights on numbers, Intel and most of its competitors began to use trademark-acceptable names such as Pentium for subsequent generations of processors, but the earlier naming scheme remains as a term for the entire family.

Minicomputers during the late 1970s were running up against the 16 bit 64k byte address limit as memory became cheaper to install. Most minicomputer companies redesigned their processors to fully handle 32 bits addressing and data. But the Intel 8086 would instead adopt a much criticized stopgap concept of segment registers which effectively raised the memory address limit by 4 bits from 16 bits / 64K to 20 bits / 1 megabyte. Data and code could be managed within “near” 16-bit segments within a larger 1M address space, or a compiler could operate in a “far” mode using both segment and offset. While that limit would also prove to be too small by the mid 1980s, it was ideal for the emerging PC market, and made it very simple to translate software from the older 8080 to the newer processor.

As hardware has evolved, the architecture has twice been extended to a larger word size. In 1985, Intel released the 32-bit 386 to replace the 16-bit 286. The 32-bit architecture is called x86-32 or IA-32 (an abbreviation for Intel Architecture, 32-bit). In 2003, AMD introduced the Athlon 64, which implemented a further extension to the architecture to 64 bits, variously called x86-64, AMD64 (AMD), EM64T or IA-32e (Intel), and x64 (Microsoft), not to be confused with IA-64.Contents

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