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CPU (Central Processing Unit) Chip: Cooling Problems, Requirements and Solutions

Clifford T. Johnson, P.E., CSE

Course Outline

The course will answer several questions that bother anyone who specify, use or assemble their own present day personal or industrial computers. It will answer the question, why does a computer need that noisy fan(s), how hot can the CPU (Central Processing Unit) get without causing a problem, where can I find the best solution. The course will even show you how to assembly a very simple solution to the fan noise.

This is a 2-hour course and will cover the following:

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

At the conclusion of this course, the student will:

Intended Audience

Anyone that specifies, assembles, or uses personal or industrial computers, including IT professionals and specifically Control System Engineers.

Benefit to the Audience

Course Introduction

Back in the days of 486 CPUs with clock speeds of up to 50 MHz, PC processors got along fine without any cooling devices, and nobody paid much attention to CPU cooling. The first x86 CPU in which a heatsink was recommended (but not necessarily required) was the 486DX2-66. Over the years, the power usage of CPUs has been increasing constantly, and today, where even many graphics chips need coolers, a CPU without a heatsink is unthinkable. Reason enough to have a closer look at the technology behind heatsinks. As A Control Engineer I began assembling Industrial computers many years ago and found that the fans were a source of constant maintenance and noise. I learned with the Pentium 100 that the proper sized heat sink would eliminate the major cause of crashes. Present day processors require much diligence in the sizing and proper installations of these modern coolers that now take a variety of forms. I have assembled several web sites for you to study and take the guesswork out of a potential computer weak point.

Course Content

I will add my comments to those among the following web sites that contain the majority of the course.

First you must visit “ Heat Sink Test Results by Joe Citarella.  Here you will learn the vast differences between the various coolers in the market place, Heatpipes are becoming quite commonplace.  You will also learn what to expect from your system. To calculate what to expect, for every watt the CPU radiates, the heatsink will cool the core by the (C/W x watts) plus ambient temp. For example, at a fan inlet temp of 25 C, a C/W of 0.25 with a CPU radiating 50 watts means that the CPU temp will be 37.5 C

Next I direct you to where you will find specification for many CPUs in the market:
Voltage; Absolute Maximum Voltage; Typical Amperage; Maximum Amperage: Maximum Power Dissipation;
Maximum (CPU) Case Temp. Please note that the 'Max. Case Temp.' is the maximum temperature allowable as measured on the exterior of the processor package in the middle directly above the chip die (under the heatsink). It is not the maximum internal ambient temperature of the system enclosure. The term 'case' refers to the processor's package, not the system case. The site also provides links to most CPU manufactures (none of the links on this page are included in this course) Of course the primary reason for reviewing and saving this site is that it provides the maximum operating temperature of CPUs.

The typical power dissipation of a CPU is the average value of all of the computers parts while running the worst-case instruction sequence.

The next site has a wealth of information.  covers: Maximum CPU Operating Temperatures Thermal interface materials, costs, and the best to use. Case (and this time I mean the enclosure, not the CPU case) cooling Some tips on how you can reduce the noise of fans using 7 volts. A convenient air flow conversion table.

Once you have digested the information above I would like you to go to  Heatsink Mounting Pressure vs Performance
This site has a very good explanation of the Thermal effects of a heatsink.

Then jump to  "Aircooled Heatsink Roundup" by Joe Citarella

By now you should have a good understanding of Heatsinks and fans and should be able to choose the proper cooling device for your CPU and install it, BUT you may not appreciate the noise it can cause. Let’s go to The Listening Room at here you can hear the sound that various fans make, if you have a cable, DSL or similar high-bandwidth connection. You will find out that the size or the capacity of the fan does not determine the sound it makes.  The Heatsink itself will impart a sound based on the velocity of the air passing through its leaves.

OK, now for the final bit of education, it’s time to introduce you to a little know fact, how you can make a simple fan controller. Can you take it to the final challenge and assemble the controller?

Course Summary

In order to select a proper cooling device for modern CPUs this course will be an invaluable aid and could ultimately prevent a toasted chip, or at the least elevate the annoyance of a noisy fan. Each of the sites used can provide choices of coolers from standard fan/heatsink through heat pipes and water coolers.


Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

Take a Quiz

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.