X86

x86 is an instruction set architecture (ISA) for the Intel 8086 microprocessor, a chip which was first produced in the late 1970's (get exact date) and is notable for being the chip used in the very first IBM compatible PC sold by IBM beginning in 1983. Remarkably, around this time Intel and Microsoft jointly made a decision to maintain backward compatibility in both hardware and software, with the result that all subsequent "Intel" processor chips could always execute the original x86 instructions. Furthermore, this joint decision meant that any program which ran on the original Microsoft DOS operating system, whose hardware platform was always guaranteed to be x86, continued to execute successfully on later versions of Microsoft operating systems.

This decision to maintain backward compatibility of hardware and software laid the groundwork for the subsequent success of the x86 family of microprocessors, and the IBM compatible PC's which contain them.