The history of the processor, part I

286

In February 1982 unleashed a true revolution when they released the 286 processor. The 186 was never popular in consumer PC's, but the 286 was immediately adopted by IBM to use in their IBM PC AT, the successor to the XT that had the 8088 as processor. The new 16 bit 286 sported 134.000 transistors and proved to be around 20 times faster than the 8088. The 286 came in three speeds; 6, 10 and 12 MHz. Not only the increase in clockspeed made the processor a lot faster than the 8088, it was also a ot more effecient. The 8088 needed 12 clockcycles to finish an instruction, the 286 only needed 4,5. The 16 bit databus ensured a faster communication with the memory, which helped the overall performance of the system.

As all past and current Intel processors the 286 was compatible with the 8086/8088 and all software written for the XT could run without problems on the 286. A lot of users however will remember that all games originally written for the 8088 ran too fast on the 286 PC's. This was a bit of a lucury prblem though, as the new 286 had a lot more possibilities than its predecessor; not only was it capable of addressing 16MB of memory (something that was utterly unaffordable at the time), it could also use vurtual memory. A part of the hard disk could be used as additional memory for programs, but to use more than 1 MB of memory certain drivers had to be used and the processor had to switch to a new mode called "protected mode". When in protected mode the 286 functioned as a multitasking processor, this was also a first. Parts of programs in the memory were protected against the parts of other programs, so these could run at the same time. The operating system of the time, DOS, could not use this protected mode, and ran in "real mode"; this basically means that the 286 under DOS was nothing else than a fast 8088.

A 286 processor had 68 pins. Intels current processors have no less than 775.

32-bit at last!

Topping the release of the 286 was the introduction of the 386DX processors in 1985. The 386 was the first 32 bit processor, which opened up new possibilities. Because of the 32 bit address bus the 386 was capable of addressing 4GB of memory, and true to Moore's law Intel increased the number of transisitors on the chip to 275.000. The 386 has been released in clockspeeds of 16, 20, 25 and 33 MHz between 1985 and 1989, and could work in real mode and in protected mode, same as the 286. A new mode was the "virtual real mode", this enabled the processor to run several real mode sessions at the same time and could mutitask even with older software. The Windows versions that were released in that period used this mode, but the DOS version could not, as this was a 16 bit operating system. As you know up to Windows 95 the operating system was still mostly 16 bit, which means that the software was not ready for the 386 till 10 years later. The OS/2 operating system developed for IBM PC's was a fully 32 bit system and could use all possibilities of the 386, however this never took off as they thought it would. This time it was not IBM that built the first PC with the new processor, but a company named Compaq.

The real mode performance of the 386 was similar to that of the 286, the 386 needed 4,5 clockcycles to finish an instruction. In protected mode the new processor was a lot faster, mainly due to the advanced memory manangement unit in the processor.

Intel decide to release a budget version of the 386 in 1988, the 386SX. Thsi processor still ran at 32 bits internaly, but had an external 16 bit databus. This meant that the processor could only address 16MB of memory, still more than ample at the time. The time that 16MB was a standard in home PC's was still years away at the introduction of the 386SX. Because of its low price the 386 quickly became very popular, its performance was on par with that of the 386DX and the possibility to run more than one DOS program in virtual mode caused the 386SX to take the place of the 286. The 386SX processor could work on a slightly modified AT motherboard, which made it cheap for manufacturers to produce the PC's.

The worlds first 32 bit processor, the Intel 386DX

Coprocessor

The 8088, 286, 386 and 486SX processors could only calculate with complete numbers (integers), they were able to handle floating point calculations as well, but this needed some tricks and therefore did not operate very fast. Scientific companies however did require a processor to handle floating point calculations, and to fulfill thi sneed Intel designed the Coprocessor. This was an extra chip that could be placed on the motherboard and take over all floating point calculations from the main processor. Intel designed three version of this coprocessor, the 8087 for he 8088.86, the 287 for the 286 and the 397 for the 386. When the 486DX was introduced the coprocessor was integrated on the die. Software had to especially designed tomake use of the coprocessor, the first versions of for instance AutoCAD was suitable for it, however normal comsumers had very little use for the add-on coprocessors. Next to Intel another firm designed coprocessors for the 386, a company called Weitek. Their version of the coprocessor worked a lot faster than Intel's own, however was not compatible with existing software.