Not all Pentiums are alike

Computer Basics, Hardware Issues

Question: Could you please explain the difference between the Pentium processor and the 586 or 686? I thought a Pentium 166 Mhz was the top of the line, but I just heard that 686s are faster. Why did Intel go away from the x86 name? – Glen

Answer: That’s a very big question, but in short, here are some answers from several sources.

Intel’s chip name change: The company wanted a trademark name so they switched from numbers to names for their processors. Only Intel can sell you a “Pentium” or “Pentium Pro” processor. Other manufacturers have to name their chips something else.

Many people use the term “586” interchangeably with “Pentium” since it’s obviously the successor to Intel’s 486. Other chip manufacturers such as Cyrix, AMD and NexGen use the number 586 to indicate rough equivalence to the Pentium.

The term “686” is often used with reference to the Pentium Pro, the next generation of Intel’s x86 chip family. Again, many of Intel’s competitors use the number 686 in the naming of their roughly equivalent processors.

As for the difference between a Pentium and Pentium Pro, that’s a can of worms. Put your fishing cap on (watch out for those hooks), and let’s open it.

The Pentium Pro has a 256KB secondary cache built in, rather than as an external option, as it is on the Pentium (cache is a portion of high–speed static memory that stores frequently used commands). It’s built–in status on the Pentium Pro means it can run at the processor’s faster internal clock speed (200MHz on a 200MHz Pentium Pro) rather than at 66Mhz, the speed of the slower external bus. (The external bus is a collection of wires through which data is transmitted from one part of a computer to another.)

The Pro also has lots of internal improvements including:

  • a deeper instruction pipeline
  • multiple arithmetic units
  • better branch prediction logic
  • register renaming

Without going into this too deeply and driving you absolutely insane with techno–terms, these features allow the processor to execute more instructions per clock cycle. That makes it zippier. When it runs 32–bit applications that are calculation–intensive, Pentium Pro typically runs about 1.5 times as fast as a Pentium of the same clock–speed (which is measured by the Mhz rating).

Some of the Pentium Pro’s drawbacks: Intel decided to optimize the chip for 32–bit rather than 16–bit code. So 16–bit DOS and Windows applications suffer a bit. You might know that 16–bit code moves across the computer in chunks half as big as 32–bit code. A 200 Mhz Pentium Pro may only achieve the speed of a 150 Mhz or 160 Mhz Pentium with 16–bit software. Meanwhile, many DOS and Windows programs are already 32–bit so they benefit from the Pro.

TechnologyTips Note: Since the writing of this article, processors have grown dramatically in there speed and power. If you are in the market for a new processor, you can visit [link removed].com to find one that fits your needs. Remember that Intel isn’t the only big name anymore. AMD is one of the leaders in manufacturing them as well.