Released in 1978, the 8086 began the long line of Intel’s most successful architecture, which eventually included the 80286, 80386 and 80486. The 8086 was a 16-bit processor with a 16-bit data bus, 20-bit external bus, 64K I/O ports; it ran at up to 10Mhz.
In the previous processor generation the amount of addressable RAM was 64K. The 8086 was designed to address as much as 1MB of memory. Normally, a 16-bit processor is limited to 64KB of RAM; while the 8086’s 20-bit bus made 1MB possible, it still needed a way to address it with a 16-bit processor. The 8086 achieved this by transitioning from flat address space to segmented memory.
Rather than redesign the entire memory system, Intel modified it by using a two-part, compound 16-bit address. The memory management unit (MMU) then interpreted the specified 64K segment, as well as its offset, to find the physical address. Once the address was located, the MMU would enquire if the memory permissions allowed the request and, if they did, perform it.
Since the days of the 8086 many companies have made cloned or enhanced versions of it and other Intel processors. These manufacturers include AMD, Texas Instruments, OKI, Siemens AG, NEC and Mitsubishi.