Intel 80386, a microprocessor used as the CPU of many personal computers from 1986 til 1994. During its design the processor was code-named simply "P3" -- the third-generation processor in the x86 line, but was and is frequently abbreviated i386. Designed and manufactured by Intel, the i386 processor was first taped-out in October of 1985. Intel decided against producing the chip before then, as the cost of production would have been prohibitively expensive. Fully functional 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. The 80386 brought a 32-bit architecture together with a hardware memory management unit (MMU). This was the first single chip processor that made the implementation of multiprocessing operating systems possible. Before that time, personal computers based on Intel processors were almost exclusively driven by the DOS and CP/M systems. Because of the lack of an MMU there was little point in building a file structure on pre 386 computers that differentiated between executable code and data. The inability to differentiate between executable code and data is the primary reason why computers can be infected by viruses.
Intel later introduced the 80486, but neither it nor its successors under the Pentium name were as big a step as the 32-bit flat addressing made possible by the 80386. Most applications running on personal computers in 2003 will run on the older 80386, albeit very slowly; there are only a few instructions added to the main instruction set in later generations, and in most cases their usage is unnecessary. Building a program for the 80286 is much harder, and usually requires fundamental changes to the application.
Because of the high degree of compatibility, the whole range of processors compatible with the 80386 is often collectively termed the i386 architecture; the instruction set for the architecture is 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 -- i.e. 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 -- 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.
See also List of Intel microprocessors
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