Intel 80386 Processor

关于 Intel 80386

Intel 80386（简称 386 或是 i386）是第一款用于个人电脑的 32 位中央处理器，并增加内存寻址能力到 4GB！不过 386 有两种版本，其中 SX 版的外部总线宽度只有 16 Bit 而且只支持 16 MB 内存，DX 才是 32 Bit。Intel 80386 推出没多久居然发现其中有些芯片在执行 32 位程序的时候会产生宕机的情形，所以英特尔只好把那些库存里已经封装好的芯片再进行多一项测试，并在有问题的 386 封装上面打上“16 BITS S/W ONLY”，表示此款 386 只可以用来执行 16 Bit的程序，而没有问题的晶片则被打上“ΣΣ”的符号。当然，没有人会愿意花一样的钱买一个有问题的晶片，所以数量上，拥有“16 BIT S/W ONLY”字样的 80386 极为稀少。

SL 是给笔记型电脑使用的低耗电版本，拥有 16 Bit 外部总线宽度以及 24 Bit 外部寻址能力。由于 386 并没有内建浮点运算器，所以需要大量数学运算的使用者得添购 Intel i387 数学辅助运算芯片。80386 还可以直接执行 8086 的程序喔！

MG80386 为英特尔军用 386 的机械样本（M代表军用标准温度、G代表PGA封装），军用微处理器的运作标准温度为摄氏零下 55 度至 125 度。虽然 386 听起来已经是非常老旧的产品，不过实际上，美国航天工业的最高标准（比如说美国宇航局，NASA）规定各种芯片需要有一定年数（我记得好像是十年）的使用记录才可以使用，以确定其技术的稳定性以及可预期的错误有哪些。加上严苛的运作温度要求，最新的微处理器通常不会出现在战略系统上面。美国战斧巡航导弹（Tomahawk Cruise Missile）就是使用 80386 来当作其中央处理器的。

Introduction

The Intel 80386, introduced in October 1985, was the successor to the 80286 processor and the first Intel processor with 32-bit data and address busses. It allows multiple application programs to run at the same time (when running under 386-specific operating systems) using Protected Mode. The 386 can address four gigabytes (2^32 bytes) of memory using Enhanced Mode, a 32-bit extension of Protected Mode. As it was in the 80286, segment registers were used to index inside a segment table that described the division of memory. Unlike the 286, however, inside each segment one could use 32-bit offsets, which allowed every application to access the 4GB of memory. However, 16 megabytes was a typical maximum in IBM PCs. In addition, Enhanced Mode supported paging, a mechanism which made it possible to use virtual memory.

The first IBM compatible to use the 386 was the Compaq 386, before IBM used it in high-end models of their PS/2 series.

With the 386, Intel introduced the ‘DX’ - ‘SX’ naming system. DX stands for Double-word eXternal, SX for Single-word eXternal. The SX versions therefore are lower-speed version of the 386(DX), introduced in 1989. They use a 16-bit instead of a 32-bit data bus.

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. 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 486 came in a DX variant that did include floating-point capability (while the 486SX did not).

The 80386 EX microprocessor is designed for embedded applications that require high integration and low power. Key features include power management, low-voltage operation, and on-chip integration of numerous common peripherals such as interrupt controllers, chip selects, counters and timers.

In October 1990, Intel released the 80386SL, which was basically an 855,000 transistor version of the 386SX processor, with cache, bus, and memory controllers, ISA compatibility and power management circuitry. It added a special system management mode (SMM), in which the BIOS could more easily perform power management and other functions without requiring OS support. The 386SL was the first chip specifically made for portable computers.

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