CPU - Old Intel Processors

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-C.Haines 7/99

Pentium Classic

-Most of us remember the Pentium and the revolution it made to the personal computer industry. Pentium seems to be the leader in this market and will most likely remain so for years to come. So what's behind the Pentium classic and why did people flip to buy one?

-In March 1993 Intel shipped the first Pentium CPU's to vendors and it was a big deal to say the least. This CPU was the first x86 CPU to provide Superscalar Pipelining which allowed the CPU to use to pipes to pump more than one set of instructions out at a time. This was a good boost for the consumer computer. There was however some problems when they first made it out there in the real world.


-The 60 and 66 MHz CPU's created a vast amount of heat and sucked up 16 watts during normal operation. Even the newer CPU's just slightly after these were power hungry and ran very hot. Intel did however shrink the CPU and allow for better cooling and boosted the clock rates up to 75, 90, and 100 MHz.

-Within two short years clock speeds were doubled but were still running at 3 times the speed of the motherboard. Of course this isn't Pentium's fault but it took time for manufacturers to boost Bus speeds and better lines of communication on the motherboard, as now you can see that we have 100Mhz Bus speed operation versus the 60 and 66 MHz speeds.

Goodies On The inside

-Better than just faster clock speeds we were looking at a 64 bit external data bus and 16kb of L1 cache. Also 8kb was dedicated to data and instructions on the cache, making things even better. Another added feature to the Cache was a improvement from the 486, this allowed out going data to be stored which saved the CPU from taking data in and writing back to main memory. Another way of freeing up CPU time.

-Other than cache improvements of the 486 the Pentium provided twin pipelines as mentioned before. This was also a five stage process that included pre-fetching, instruction decoding, address generation, execution, and write back. This came down to the CPU being able to do its work while at the same time it gathered or pre fetched information for later use.

Its Smarter

-We all know the CPU is a fairly smart device well the classic wasn't to dumb either. It also employed what is called branch prediction, this attempts to get the right bits into the right pipelines. We don't want data in the addressing pipeline now do we? The process was also looked after from the branch target buffer which basically examined past usage and codes.

-The Floating Point Unit in the 486 wasn't to great so the Classic also improved this feature. The FPU is mainly for those high mathematical programs such as image editors, CAD/CAM and so on. The faster FPU really help make the way for more software makers and there programs.

-To close this section I will also add that there were many improvements in these processors from the 486 but the specs didn't change much till MMX. Take a look at the Classic Spec's and see the difference over the two year period.


1st Gen

2nd Gen

3rd Gen

-Clock Speed 60,66 MHz 75,90 MHz 120,133,166 MHz
-L1 Cache 8kb/8kb 8kb/8kb 8kb/8kb
-L2 Cache Speed 60,66 MHz 60,66 MHz 60,66 MHz
-Pipelines Two Two Two
-Data Bus int/ext 32-bit/64-bit 32-bit/64-bit 32-bit/64-bit
-Transistors 3.1 Million 3.3 Million 3.3 Million
-Manf. Process .8 Micron .6 Micron .35 Micron
-Pin Count 273 296 296


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