x86 is the generic name of an architecture of
microprocessors first developed by
Intel.
History
The x86 architecture first appeared inside the
Intel 8086 CPU in
1978. It was adopted (in the simpler
8088 version) three years later as the standard CPU of the
IBM PC. The PC's enormous success during the last 20 years has guaranteed that the x86 architecture that became the most popular CPU architecture ever. See also
Intel.
Design
It can be generalized that the x86 architecture is CISC with variable instruction length. However most of its aspects evolved through the years, while retaining backwards compatibility.
Real mode
Intel 8086 and
8088 had 14 16-bit registers. Four of them (AX, BX, CX, DX) were general purpose (although each had also an additional purpose; for example only CX can be used as a counter with the
loop instruction). Each could be accessed as two separate bytes (thus BX's high byte can be accessed as BH and low byte as BL). In addition to them, there are 4 segment registers (CS, DS, SS and ES). They are used to form a memory address. There are 2 pointer registers (SP which points to the bottom of the stack, and BP which can be used to point at some other place in the stack or the memory). There are two index registers (SI and DI) which can be used to point inside an array. Finally, there are the flag register (containing flags such as carry
?, overflow
?, zero and so on), and the instruction pointer (IP) which points at the current instruction, and can't be changed directly.
Manufcaturers
x86 and compatibles are manufactured by:
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