Which Pentium is Which?

Kenn's
Tech
Notes

19980401: Which Pentium is Which?

April/1998
Tech Note #1

Tip of the Month! Al F gives us our April/98 tip of the month. When installing Pentium motherboards or upgrading CPUs on Pentium motherboards, you almost always have to change jumper settings based on the requirements of the CPU type. It was tough enough keeping this straight with the 486 series (SX/DX, 25, 33, 40, 66, 66 overdrive, 100 overdrive, 100 overdrive replacement, SL-enhanced, etc. etc.), but the Pentium series has an even wider range of variables. Pentiums come in a variety of speeds, frequency ratios, packages, and voltages. Although most have single-plane voltages, the new MMX Pentiums use a dual-plane voltage configuration in which different portions of the chip run at different voltages (the core runs at a lower voltage to allow higher speeds and lower power consumption). This can make it tough to decide which is the appropriate jumper setting.

If you were hoping that this second paragraph would be a quick and easy way to answer all your questions, you may be disappointed. However, as long as you have access to the Internet, you do have quick access to all the answers. Intel maintains several pages at their website with the latest information about Intel microprocessors. The Pentium Processor FAQ is very informative. For deciphering the codes stamped on the top and bottom of the chips there is a good chart. For deciding the appropriate core frequency and bus frequency settings, Intel's Quick Reference Guide is invaluable.

For complete details on the chip you are trying to install, refer to the above-noted documents.

Two items of note, culled from the Intel documents:

a. P55C refers to the line of Pentiums with MMX technology, to distinguish them from the P54C line. Make sure the motherboard you are using supports P55C processors before installing a Pentium with MMX technology on it.

b. A marking you often find on the bottom of newer Pentiums is S????/abc, where the S???? part is the S-Spec number you need for the Quick Reference Guide mentioned earlier. The abc part after the "/" will be something like VMU, or VSS, or SMS. What's helpful to realize here is that the first of the three letters refers to the voltage requirement. If the manual for the motherboard specifies different settings for VRE and STD voltages, look for this marking. If the first of the three letters is a V, set the board for VRE. If the first of the three letters is an S, set the board to STD.

DISCLAIMER: This document is intended for the reference of computer support personnel within Winnipeg School Division No. 1. There is no warranty or liability if procedures recommended here have an adverse affect on any systems. Use them at your own risk. Any trademarks mentioned are the property of their owners, none of whom have certified any information provided here. Opinions expressed here are personal only and do not represent the policy of Winnipeg School Division No. 1 or any other organization anywhere.

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