The Intel 80386 is a microprocessor which was used as the central processing unit (CPU) of many personal computers from 1986 until 1994 and later. During its design phase the processor was code-named simply ‘P3’ – the third-generation processor in the x86 line, but was and is frequently referred to as the i386. Designed and manufactured by Intel, the i386 processor was taped-out in October of 1985. Intel decided against producing the chip before then, as the cost of production would have been uneconomic. Full-function chips were first delivered to customers in 1986. Motherboards for 386-based computer systems were highly elaborate and expensive to produce, but were rationalised upon the 386’s mainstream adoption.

The processor was a significant evolution in 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 which used virtual memory.

Intel later introduced the 80486, but not until the introduction of EM64T in 2004 did Intel's processors introduce as important a feature as the 32-bit flat addressing made possible by the 80386. (Other microprocessor architectures, such as the Motorola 68000, had long since supported this form of addressing.) Most applications running on current Intel-based personal computers will still run on the older 80386, albeit very slowly; there were relatively few instructions added to the main instruction set in later generations, and in most cases their usage can be avoided. Building a program for the 80286 was often much harder.

Late in the 80386’s production run, Intel introduced the 80386SX, which was meant to be a low cost version of the i386. The SX series of chips was 32-bit internally, but had a 16-bit external bus (in much the same way that the 8088 in the original IBM PC was a lower cost version of the 8086). The original 80386 was subsequently renamed the 80386DX to avoid confusion. Also, due to this new 16-bit bus, Intel released a version of the 80386 called SX Now! which was pin-compatible with the 80286. This enabled many 80286 owners to upgrade to the 80386 without buying a new motherboard.

Because of the high degree of compatibility, the range of processors compatible with the 80386 is often collectively termed the i386 architecture; the instruction set for the architecture is now known as IA_32 or, informally, i386.

From a business perspective, the i386 was significant because it was the first significant microprocessor to be single-sourced – it was available only from Intel Corp. Prior to this, the difficulty of making chips and the uncertainty of reliable supply required that any mass-market semiconductor be multi-sourced, that is, made by two or more manufacturers, the second and subsequent ones manufacturing under license from the designer. Single-sourcing the i386 allowed Intel greater control over its development and substantially greater profits in later years. However, AMD introduced its compatible Am386 processor in March 1991 after overcoming legal obstacles, thus breaking Intel’s monopoly.

External links

Intel 80386 images and descriptions at cpu-collection.de (http://www.cpu-collection.de/?tn=1&l0=cl&l1=386)