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Intel 8086
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Intel 8086 KL Intel D8086.jpg
Produced From 1978 to 1990s
Common manufacturer(s)

Intel, AMD, NEC, Fujitsu, Harris (Intersil), OKI, Siemens AG, Texas Instruments, Mitsubishi.

Max. CPU clock rate 5 MHz to 10 MHz
Min. feature size 3μm
Instruction set x86-16
Predecessor (8080)
Successor 80186
Package(s)

40 pin DIP

Variant 8088

The 8086[1] (also called iAPX 86) is a 16-bit microprocessor chip designed by Intel between early 1976 and mid-1978, when it was released. The 8086 gave rise to the x86 architecture of Intel's future processors. The Intel 8088, released in 1979, was a slightly modified chip with an external 8-bit data bus (allowing the use of cheaper and fewer supporting logic chips[2]), and is notable as the processor used in the original IBM PC. Contents

1 History
1.1 Background
1.2 The first x86 design
2 Details
2.1 Buses and operation
2.2 Registers and instructions
2.3 Flags
2.4 Segmentation
2.4.1 Porting older software
2.5 Performance
2.6 Floating point
3 Chip versions
3.1 Derivatives and clones
4 Hardware modes
5 Peripherals
6 Microcomputers using the 8086
7 Notes and references
8 External links

History
Background

In 1972, Intel launched the 8008, the first 8-bit microprocessor.[3] It implemented an instruction set designed by Datapoint corporation with programmable CRT terminals in mind, that also proved to be fairly general purpose. 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).

Two years later, Intel launched the 8080,[4] employing the new 40-pin DIL packages originally developed for calculator ICs to enable a separate address bus. It had an extended instruction set that was source- (not binary-) compatible with the 8008 and also included some 16-bit instructions to make programming easier. The 8080 device, often described as the first truly useful microprocessor, was eventually replaced by the depletion-load based 8085 (1977) which could cope with a single 5V power supply instead of the three different operating voltages of earlier chips.[5] Other well known 8-bit microprocessors that emerged during these years were Motorola 6800 (1974), General Instrument PIC16X (1975), MOS Technology 6502 (1975), Zilog Z80 (1976), and Motorola 6809 (1978). The first x86 design

The 8086 project started in May 1976 and was originally intended as a temporary substitute for the ambitious and delayed iAPX 432 project. 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. 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).

Marketed as source compatible, the 8086 was designed to allow assembly language for the 8008, 8080, or 8085 to be automatically converted into equivalent (sub-optimal) 8086 source code, with little or no hand-editing. The programming model and instruction set was (loosely) based on the 8080 in order to make this possible. However, the 8086 design was expanded to support full 16-bit processing, instead of the fairly basic 16-bit capabilities of the 8080/8085.

New kinds of instructions were added as well; full support for...
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