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.^[2]

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.^[3]