Intel 80386
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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 first personal computer to make use of the 386 was designed and manufactured by Compaq[1], and Andy Grove, Intel's CEO at the time, made the decision to single-source the processor, decisions that were ultimately crucial to both the processor's and Intel's success in the market.
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.
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Architecture
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.
The 80386 featured three operating modes: real mode, protected mode and virtual mode. In the real mode, the 80386 (like the 80286) would run just as a fast 80186. The protected mode allowed the use of all the possibilities of the 286 and the protected mode extension of the 386, especially addressing up to 4 GB of memory. Finally, the virtual 8086(or V86) mode made it possible to run one or more virtual 8086 machines in a protected environment. Image:80386DX arch.png
Though Intel would shortly introduce the 80486 and eventually the Intel Pentium line of processors, the support in the 386 for the 32-bit flat memory model would be arguably the most important feature change until the release of EM64T in 2004. (Other microprocessor architectures, such as the Motorola 68000, had long since supported a "flat" 32-bit addressing model.) 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.
Early 80386s had a bug in the 32-bit multiply instruction which would leave the high word in the result undefined. Once discovered, such processors were stamped '16-bit SW only'. This bug was checked for by programs such as Microsoft Windows which would issue a warning message.
Variants
Late in the 80386's production run, Intel introduced the 80386SX, which was meant to be a low cost version of the 386 line. 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) and so no 32-bit physical address space extension. The original 80386 was subsequently renamed the 80386DX to avoid confusion. Neither CPU included a math coprocessor (most motherboards included a socket for an 80387), though the naming would cause some head-scratching later when the 80486 came in a DX variant that did include floating-point capability (which was physically present but disabled in early 486SXs).
The 386SL was introduced as an alternative processor for laptop computers. The processor offered several power management options (e.g. SMM), as well as different "sleep" modes to conserve battery power. It also contained support for an external cache of 16 to 64 KB. The extra functions caused this variant to have over 3 times as many transistors as the 386DX. The 386SL was only available in one clock speed, 25 MHz. [2]
An embedded version of the chip, the 386EX, was produced later, and was successfully used in space applications. Image:Am386DX40.jpg
Business Importance
The first PC company to design and manufacture a PC based on the 386 was Compaq, rather than IBM, which had been dominant until that time. IBM was offered use of the processor, but relied instead on earlier processors to which it had manufacturing rights. The success of the Compaq 386 PC played an important role in creating the PC "clone" industry, and to establishing Intel (and Microsoft) as central component suppliers to it.
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 ending Intel's monopoly on 32-bit 386-compatible processors.
Team
- John Crawford, chief architect
- Jim Slager, chief engineer
- Patrick Gelsinger
- Riaz Haq
- Gene Hill
- Jan Wiliam L. Prak
- David Vannier
- Joseph "Chip" Krauskopf
- Ken Shoemaker
- Paul Ries
- Saurabha Radhika
External links
- Intel 80386 images and descriptions at cpu-collection.de
- Intel 80386 Programmer's Reference 1986
- Intel Technology
- CPU-INFO: 80386, indepth processor history
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