Intel 80386, also known as the i386

The Intel 80386, also known as the i386, or just 386,1 was a 32-bit microprocessor introduced by Intel in 1985. The first versions had 275,000 transistors and were used as the central processing unit (CPU) of many personal computers and workstations. As the original implementation of the 32-bit extensions to the 8086 architecture, the 80386 instruction set, programming model, and binary encodings are still the common denominator for all 32-bit x86 processors. This is termed x86, IA-32, or the i386-architecture, depending on context.

The 80386 could correctly execute most code intended for earlier 16-bit x86 processors such as the 80286; following the same tradition, modern 64-bit x86 processors are able to run most programs written for older chips, 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 launched in October 1985, and full-function chips were first delivered in 1986.vague Mainboards for 80386-based computer systems were at first expensive to buy, but prices were rationalized upon the 80386's mainstream adoption. The first personal computer to make use of the 80386 was designed and manufactured by Compaq.

In May 2006, Intel announced that production of the 80386 would cease at the end of September 2007.4 Although it has long been obsolete as a personal computer CPU, Intel and others had continued to manufacture the chip for embedded systems. Embedded systems that utilise a 80386 or one of its derivatives are widely used in aerospace technology.

The processor was a significant evolution in the x86 architecture, and the latest of a long line of processors that stretched back to the Intel 8008. The predecessor of the 80386 was the Intel 80286, a 16-bit processor with a segment-based memory management and protection system. The 80386 added a 32-bit architecture and a paging translation unit, which made it much easier to implement operating systems that used virtual memory. It also had support for hardware debugging.

The 80386 featured three operating modes: real mode, protected mode and virtual mode. The protected mode which debuted in the 286 was extended to allow the 386 to address up to 4 GB of memory. The all new virtual 8086 mode (or VM86) made it possible to run one or more real mode programs in a protected environment, although some programs were not compatible.

The 32-bit flat memory model of the 386 would arguably be the most important feature change for the x86 processor family until AMD released x86-64 in 2003.

Chief architect in the development of the 80386 was John H. Crawford.5 He was responsible for the 32-bit extension of the 80286 architecture and instruction set, and he then led the microprogram development for the 80386 chip.

The 80486 and Intel Pentium line of processors were descendants of the 80386 design.