Intel 8086
The 16-bit microprocessor that launched the x86 architecture.
The Intel 8086, also called the iAPX 86, is a 16-bit microprocessor with a complex instruction set that Intel first released in June 1978. This chip launched the x86 instruction set architecture, which would become Intel’s most successful product line and a standard in modern desktop computers. Its successor, the Intel 8088, arrived in 1979 with an external 8-bit data bus, a change that allowed it to work with cheaper and fewer support chips. The x86 architecture later served as the foundation for both x86-64 and IA-64; x86-64 remains the underlying instruction set for modern CPUs like the Intel Core and AMD Ryzen. To mark the 40th anniversary of the 8086’s release, Intel issued a special edition processor, the Core i7-8086K, on June 5, 2018.
Intel’s first 8-bit microprocessor, the 8008, launched in 1972. It used an instruction set originally designed by Datapoint Corporation for programmable CRT terminals, which turned out to be fairly general-purpose. Because Intel was primarily a DRAM manufacturer at the time, the 8008 came in a small 18-pin “memory package” that lacked a separate address bus, requiring many additional ICs to build a functional computer. Two years later, Intel introduced the 8080 in a 40-pin DIL package originally developed for calculator ICs, which enabled a separate address bus. Its extended instruction set was source-compatible with the 8008 (not binary compatible) and added some 16-bit instructions for easier programming. The 8080 was later replaced by the 8085 in 1977, which used depletion-load technology and a single +5 V power supply instead of the three different voltages needed by earlier chips. Other notable 8-bit microprocessors from this era include the Motorola 6800 (1974), General Instrument PIC16X (1975), MOS Technology 6502 (1975), Zilog Z80 (1976), and Motorola 6809 (1978).
Development of the 8086 began in May 1976, initially as a temporary stand-in for Intel’s ambitious but delayed iAPX 432 project. The goal was to draw attention away from the 16-bit and 32-bit processors being developed by Motorola, Zilog, and National Semiconductor. Although the 8086 was a 16-bit microprocessor, its architecture closely resembled that of Intel’s 8-bit chips (8008, 8080, and 8085), allowing assembly language programs written for those 8-bit processors to migrate seamlessly.
Quick Facts
- Produced-Start
- June 1978
- Produced-End
- 1998
- Slowest
- 5
- Slow-Unit
- MHz
- Fastest
- 10
- Arch
- x86-16
- Predecessor
- Intel 8085
- Variant
- 8088
- Successor
- 80186 and 80286 (both of which were introduced in early 1982)
- Co-Processor
- Intel 8087, Intel 8089
- Data-Width
- 16 bits
Facts from the source article.
Lore & Background
Development of the 8086 began in May 1976, originally as a temporary substitute for the ambitious but delayed iAPX 432 project. It was an attempt to draw attention from the 16-bit and 32-bit processors of other manufacturers—Motorola, Zilog, and National Semiconductor. The architecture was defined by Stephen P. Morse with help from Bruce Ravenel in refining the final revisions; logic designers Jim McKevitt and John Bayliss were the lead engineers, and Bill Pohlman was the project manager.
The 8086 used a similar architecture to Intel's 8-bit microprocessors (8008, 8080, and 8085), allowing assembly language programs written for 8-bit chips to migrate seamlessly. New instructions and features were added, including signed integers, base+offset addressing, self-repeating operations, and microcode instructions for multiply and divide. The bus structure was designed to be flexible to anticipate coprocessors such as the 8087 and 8089. The first revision of the instruction set and high-level architecture was ready after about three months, and the chip took a little more than two years from idea to working product.
The 8086 was sequenced using a mixture of random logic and microcode, implemented with depletion-load nMOS circuitry. It was later moved to HMOS, then HMOS-II, HMOS-III, and eventually a fully static CMOS version for battery-powered devices. The original chip measured 33 mm² with a minimum feature size of 3.2 μm. The MUL and DIV instructions were very slow due to being microcoded, so programmers often used bit shift instructions instead. The 8086 was die-shrunk to 2 μm in 1981, correcting a stack register bug; later 1.5 μm and CMOS variants were outsourced to other manufacturers.
Reader's Guide
The 8086's legacy is enduring in the basic instruction set of today's personal computers and servers. It gave rise to the x86 family, which served as the foundation for both x86-64 and IA-64, with x86-64 being the underlying ISA for modern CPUs such as the Intel Core and AMD Ryzen. The 8086 also lent its last two digits to later extended versions of the design, such as the Intel 286 and the Intel 386, all of which became known as the x86 family. The PCI Vendor ID for system devices produced by Intel is 8086. An anniversary processor, the Core i7-8086K, was released on June 5, 2018, celebrating the 40th anniversary of the 8086's release. Its successor, the Intel 8088, was released in 1979 as a slightly modified chip with an external 8-bit data bus, designed for use with cheaper and fewer supporting ICs.
Did You Know?
- The 8086 was originally developed as a temporary substitute for the delayed iAPX 432 project.
- The 8086's instruction set was designed with a software-centric approach to assist source code compilation of nested functions in ALGOL-family languages like Pascal and PL/M.
- The 8086 could operate in either minimum mode (for single-processor systems) or maximum mode (for multiprocessor systems, required when using an 8087 or 8089 coprocessor).
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