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I386

Intel 386
KL Intel i386DX.jpg
Intel 80386 DX rated at 16 MHz
Produced From October 1985 to September 2007
Common manufacturer(s)
  • Intel
  • AMD
  • IBM
Max. CPU clock rate 12 MHz to 40 MHz
Min. feature size 1.5µm to 1µm
Instruction set x86 (IA-32)
Predecessor Intel 80286
Successor Intel 80486
Co-processor Intel 80387
Package(s)
  • 132-pin PGA, 132-pin PQFP; SX variant: 88-pin PGA, 100-pin PQFP
Intel 80386 registers
31 ... 15 ... 07 ... 00 (bit position)
Main registers (8/16/32 bits)
EAX AX AL Accumulator register
EBX BX BL Base register
ECX CX CL Count register
EDX DX DL Data register
Index registers (16/32 bits)
ESI SI Source Index
EDI DI Destination Index
EBP BP Base Pointer
ESP SP Stack Pointer
Program counter (16/32 bits)
EIP IP Instruction Pointer
Segment selectors (16 bits)
  CS Code Segment
  DS Data Segment
  ES ExtraSegment
  FS F Segment
  GS G Segment
  SS Stack Segment
Status register
  17 16 15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00 (bit position)
  V R 0 N IOPL O D I T S Z 0 A 0 P 1 C EFlags

The Intel 80386 ("eight-oh-three-eighty-six"), also known as i386 or just 386, is a 32-bit microprocessor introduced in 1985. The first versions had 275,000 transistors and were the CPU of many workstations and high-end personal computers of the time. As the original implementation of the 32-bit extension of the 80286 architecture, the 80386 instruction set, programming model, and binary encodings are still the common denominator for all 32-bit x86 processors, which is termed the i386-architecture, x86, or IA-32, depending on context.

The 32-bit 80386 can correctly execute most code intended for the earlier 16-bit processors such as 8088 and 80286 that were ubiquitous in early PCs. (Following the same tradition, modern 64-bit x86 processors are able to run most programs written for older x86 CPUs, all the way back to the original 16-bit 8086 of 1978.) Over the years, successively newer implementations of the same architecture have become several hundreds of times faster than the original 80386 (and thousands of times faster than the 8086). A 33 MHz 80386 was reportedly measured to operate at about 11.4 MIPS.

The 80386 was introduced in October 1985, while manufacturing of the chips in significant quantities commenced in June 1986.Mainboards for 80386-based computer systems were cumbersome and expensive at first, but manufacturing was rationalized upon the 80386's mainstream adoption. The first personal computer to make use of the 80386 was designed and manufactured by Compaq and marked the first time a fundamental component in the IBM PC compatible de facto-standard was updated by a company other than IBM.


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