However, the 8086 design was expanded to support full 16-bit processing. The programming model and instruction set is (loosely) based on the 8080 in order to make this possible. Marketed as source compatible, the 8086 was designed to allow assembly language for the 8008, 8080, or 8085 to be automatically converted into equivalent (suboptimal) 8086 source code, with little or no hand-editing. Both the architecture and the physical chip were therefore developed rather quickly by a small group of people, and using the same basic microarchitecture elements and physical implementation techniques as employed for the slightly older 8085 (and for which the 8086 also would function as a continuation). It was an attempt to draw attention from the less-delayed 16- and 32-bit processors of other manufacturers (such as Motorola, Zilog, and National Semiconductor) and at the same time to counter the threat from the Zilog Z80 (designed by former Intel employees), which became very successful.

The 8086 project started in May 1976 and was originally intended as a temporary substitute for the ambitious and delayed iAPX 432 project. Other well known 8-bit microprocessors that emerged during these years are Motorola 6800 (1974), General Instrument PIC16X (1975), MOS Technology 6502 (1975), Zilog Z80 (1976), and Motorola 6809 (1978). The 8080 device was eventually replaced by the depletion-load-based 8085 (1977), which sufficed with a single +5 V power supply instead of the three different operating voltages of earlier chips.

It has an extended instruction set that is source-compatible (not binary compatible) with the 8008 and also includes some 16-bit instructions to make programming easier. Two years later, Intel launched the 8080, employing the new 40-pin DIL packages originally developed for calculator ICs to enable a separate address bus. The device needed several additional ICs to produce a functional computer, in part due to it being packaged in a small 18-pin 'memory package', which ruled out the use of a separate address bus (Intel was primarily a DRAM manufacturer at the time). It implemented an instruction set designed by Datapoint corporation with programmable CRT terminals in mind, which also proved to be fairly general-purpose. In 1972, Intel launched the 8008, the first 8-bit microprocessor.

Intel c compiler __sync_fetch_and_add