History
The Intel 8088 and 8086 were the first CPUs to have an instruction set that is now commonly referred to as x86. These 16-bit CPUs were an evolution of the previous generation of 8-bit CPUs such as the 8080, inheriting many characteristics and instructions, extended for the 16-bit era. The 8088 and 8086 both used a 20-bit address bus and 16-bit internal registers but while the 8086 had a 16-bit data bus, the 8088, intended as a low cost option for embedded applications, had an 8-bit data bus. The x86 assembly language covers the many different versions of CPUs that followed, from Intel; the 80188, 80186, 80286, 80386, 80486, Pentium, Pentium Pro, and so on, as well as non-Intel CPUs from AMD and Cyrix such as the 5x86 and K6 processors, and the NEC V20. The term x86 applies to any CPU which can run the original assembly language (usually it will run at least some of the extensions too).
The modern x86 instruction set is a superset of 8086 instructions and a series of extensions to this instruction set that began with the Intel 8008 microprocessor. Nearly full binary backward compatibility exists between the Intel 8086 chip through to the current generation of x86 processors, although certain exceptions do exist. In practice it is typical to use instructions which will execute on anything later than an Intel 80386 (or fully compatible clone) processor or else anything later than an Intel Pentium (or compatible clone) processor but in recent years various operating systems and application software have begun to require more modern processors or at least support for later specific extensions to the instruction set (e.g. MMX, 3DNow!, SSE/SSE2/SSE3).
Read more about this topic: X86 Assembly Language
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