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386

Designer
Manufacturers
Introduction date
Introduction speed
Maximum speed
Cache
Transistor count
Manufacturing process


: Intel
: Intel, AMD, C&T, IBM
: June1985
: 16 MHz
: 40 MHz
: -
: 275,000
: 1.5 & 1 micron


The 386 is a very important processor in the x86 CPU history. It was the very first 32 bit CPU for the IBM PC! The 32 bit architecture is still used in all current CPU's. You could say that the Pentiums and Athlons are based on the design of the 386.

When the 386 was launched in 1985 it was certainly not faster than the 20MHz and 25MHz 286's. But Intel designed many new features into the CPU that gave it many more possibilities than the 286. For instance, the 386 could operate in three modes: the Real mode to emulate a 8086/8088, the Protected mode just like the 286 and the new Virtual mode that made multitasking possible. Also new was the possibility of the 386 to switch between the three modes without having to reset. Something that was impossible for the 286.

The first 386's had a speed of 16MHz and PC's using this processor were very expensive. This was not only because the processor had a high price but also because of the peripherals. Because of the 32 bit design of the 386, new motherboards and support chips (chipsets) had to be designed. The market initially adopted the 386 very slowly, which was largely because of the price. Intel decided to introduce a cheaper version of the 386, the 386SX. This was a ordinary 386, but the 32bit databus to the motherboard was replaced by a 16bit databus. This made the design and production of motherboards cheaper and thus lowered the price of the PC's with a 386SX CPU. The 386 CPU with the 32bit databus would live on as 386DX and the version with the 16bit databus as 386SX. Intel used this strategy of making two versions of a CPU already with the 8086/8088 and the 80186/80188. The only difference between these CPU's was also the databus. I do not know why Intel chose for the SX and DX name scheme, but I do know it raised a lot of misunderstandings! With the 386 the difference between SX and DX was the databus, but with the 486 the difference was that the SX version had no co-processor and the DX had an integrated co-processor!

Both the 386DX and the 386SX did not have an integrated numeric co-processor, but these could be bought separately and most motherboards had a special socket for these co-processors. The 386 had a long market life and the PC market grew very fast, many first time buyers of a PC bought a 386. So there was money to be made in the co-processor business, what explains the relatively large availability of co-processors. Intel of course produced co-processors, but there were more companies that produced them. For instance Cyrix, ULSI, WEITEK and C&T all designed and produced numeric co-processors for the 386 market.

Intel produced 386's at a speed up to 33MHz. but AMD went on to produce at higher speeds and produced 386's at a speed of 40MHz. This AMD 386DX-40 was very popular, if there would be a prize for the bestselling CPU of all times this would be one of the candidates! One of the reasons was the speed of the CPU, when the first 486's came on the market at 16MHz they offered no more performance than the 386DX-40. So even after Intel introduced the 486 in 1989 the AMD 386DX-40 sales stayed high.

With the introduction of the 386 with its virtual mode, it was possible to run more than one application on a PC. Multitasking was born and so the basis for Windows (3.0). Although it was possible to run Windows on a 286, the 386 ran it more efficient and faster.

The 386 CPU appeared in many different packages, but mostly in CPGA and PQFP form factors. The RAM modules typically used with the 386 were 30 pin SIMM modules. Nice detail was that the 386 was introduced in a Compaq PC and not an IBM PC like all previous Intel CPU's.


All 386 pictures

 

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