Intel® Pentium® III Xeon® Processor
Thermal Management

This document is written for professional system integrators building PCs from industry-accepted motherboards, chassis, and peripherals. It provides information and recommendations for thermal management in systems using boxed Pentium® III Xeon® processors.

It is assumed that the reader has a general knowledge of and experience with workstation and server operation, integration, and thermal management. Integrators who follow the recommendations presented here can provide their customers with more reliable systems and will see fewer customers returning with problems. (The term "boxed Pentium III Xeon processors" refers to processors packaged for use by system integrators.)

Thermal management
All systems using Pentium III Xeon processors require thermal management. In this case, "thermal management" includes three major elements: (1) a heatsink properly mounted to the processor, (2) local airflow to transfer the heat to the chassis air, and (3) airflow to evacuate the heated air from the chassis. The ultimate goal of thermal management is to keep the processor at or below its maximum operating temperature. Table 1 shows the maximum operating temperatures of specific Pentium III Xeon processors. The maximum operating temperature is measured at the center of the surface of the processor's thermal plate and varies depending on the particular frequency and stepping of the processor.

Table 1. Boxed Pentium® III Xeon® Processor information

Processor Core Frequency and L2 Cache Size (MHz/Bytes) Boxed Pentium III Xeon Processor Stepping Maximum Thermal Plate Temp (°C) Power Dissipation (W)
500/512KB C0 75 36.0
500/1MB CO 75 44.0
500/2M C0 75 36.2
550/512K CO 68 34.0
550/1MB C0 68 34.0
550/2MB CO 68 39.5
600/256K A2 55 21.6
667/256K A2 55 23.9
700/1M A1 65 32.0
700/2M A1 65 32.0
733/256K A2 55 26.2
800/256K A2 55 28.5
866/256K B0 55 30.8
933/256K B0 55 33.2
1000/256K C0 55 34.6

Proper thermal management is achieved when heat is transferred from the processor to heatsink, from the heatsink to the chassis air, and from the inside the chassis to the outside. Boxed Pentium III Xeon processors are shipped with an attached high-quality heatsink, which can effectively transfer processor heat to the system air. It is the responsibility of the system integrator to ensure good system airflow to remove the heat from the heatsink, and from the chassis to the outside air

This document makes recommendations for achieving good system airflow.

Integrated heatsink
The boxed Pentium III Xeon processor is shipped with an attached high quality heatsink. Figure 1 shows the processor and heatsink.

Pentium(R) III Xeon(R) processor and Heatsink

Figure 1: Boxed Pentium® III Xeon® Processor and Heatsink

The heatsink that ships with the boxed Pentium III Xeon processor has already been securely attached to the processor. A small amount of thermal grease (already applied), or thermal interface film, provides effective heat transfer from the processor to the heatsink. Even though the heatsink is attached with normal screws, the heatsink should never be removed. Removing the heatsink will void the processor warranty. The thermal interface material (grease or film) has been efficiently placed and may not achieve the same efficiency if the heatsink is removed and replaced

The heatsink design allows heat to transfer from the processor, through the thermal interface material, through the heatsink base, and up each of the heatsink fins. Airflow around the fins carries the heat off the fins and into the chassis interior. The heatsink is designed for maximum efficiency when air flows either horizontally or vertically cross the heatsink. In some cases, air can be blown directly into the middle of the heatsink, provided that the exiting air is eventually removed form the chassis. The system integrator is responsible for removing the heat from the heatsink fins with localized airflow.

Creating localized airflow across the heatsink
Localized airflow refers to an appropriate amount of air flowing across or into the heatsink to transfer heat from the heatsink fins to the internal chassis air. There are three methods of achieving proper localized airflow on a boxed Pentium III Xeon processor:
  1. Chassis fans can create high enough airflow through the chassis, or through the processors with ducting, to eliminate the need for localized airflow.

  2. Fans placed close to the processor can draw air vertically or horizontally across it.

  3. An auxiliary fan can be attached to the heatsink face to remove the heated air.
Some chassis designs create extremely good airflow into the chassis, through the processors, and out of the chassis. Localized heatsink airflow may be created using large chassis fans and specialized ducting that directs air across each processor's heatsink. Many server designs using 2-4 processors already use ducting and large, high speed fans to create high airflow and direct them across the processors. Usually, these chassis are expensive and custom designed to fit the motherboard being used. However, such expensive systems are specifically designed to maintain system reliability, which includes keeping the processor within thermal specifications. The newly introduced WTX specification was created to standardize a new motherboard and chassis form factor, fix the relative processor location, and allow for high volume airflow through a portion of the chassis where the processors are positioned. This allows for standard form factor motherboards and chassis to be used to integrate processors with more demanding thermal management requirements. Integrators are encouraged to use WTX form factor motherboards and chassis when they are available in late 1999. Refer to the WTX specification for more information.

If the chassis fans do not create enough airflow across the processors, or do not employ ducting, localized airflow may be absolutely necessary. Localized airflow can be created using fans that attach to special chassis brackets, retention mechanisms, or the heatsink itself. Some chassis may have brackets next to or on top of the processors that are designed to hold fans that direct air locally across the processor heatsinks. Make sure chassis such as these will work with your motherboard design.

Some retention mechanisms supplied with Pentium III Xeon processor based motherboards provide locations for mounting small fans that draw air across the heatsink. Figure 2 shows an example of a second Pentium III Xeon processor being installed in a dual retention mechanism (DRM). In this example, two small fans are installed in the DRM. The fans ensure adequate airflow is directed through the second processor's heatsink.

Pentium(R) III Xeon® processor Being Installed into Dual Retention Mechanism (DRM)

Figure 2: Boxed Pentium® III Xeon™ Processor being installed into dual retention mechanism (DRM)
Note that, unlike the second processor, the first processor has no fans directly drawing air across its heatsink. Thus, the chassis fans must provide adequate airflow to cool the first processor, or a fan must be attached directly to the heatsink. The boxed Pentium III Xeon processor's heatsink(this does not apply to heatsinks designed for the 866 MHz and greater processors) was designed to accommodate an auxiliary fan, if one is necessary. The heatsink has two "channels" into which the supplied grommets can be placed. A standard 40mm fan (with 36mm mounting hole spacing) or 50mm fan can be attached with screws provided with the processor. A fan attached to the heatsink face allows heat to be removed from the heatsink fins and evacuated into the chassis air. More information on the boxed Pentium III processor's heatsink and fan attach feature can be found in the Pentium® III Xeon® Processor Datasheet.

Pentium(R) III Xeon® processor with Fan Positioned for Attachment

Figure 3: Boxed Pentium® III Xeon® Processor with Fan Positioned for Attachment

Follow the steps below to mount a fan:
  1. Position the 40mm fan over the center of the heatsink with the fan mounting holes lined up over the grommet channels, as shown in Figure 3. If using a 50mm fan, position the fan diagonally over the upper grommet channel.

  2. Insert the grommets into the channel, using the fan mounting locations as a guide. The grommets should be positioned so they will expand into the heatsink fins when a screw is inserted into them.

  3. Position the fan over the grommets and secure with screws. Only two screws are necessary to attach one fan.

  4. Attach the fan power cable to the appropriate power source, which may be either a chassis power supply connector or a special fan power header on the motherboard.

Managing system airflow
The following are factors which determine system airflow:
  • Chassis design
  • Chassis size
  • Location of chassis air intake and exhaust vents
  • Power supply fan capacity and venting
  • Location of the processor slot(s)
  • Placement of add-in cards and cables
System integrators must ensure adequate airflow through the system to allow the heatsink to work effectively. Proper attention to airflow when selecting subassemblies and building systems is important for good thermal management and reliable system operation.

Integrators use two basic motherboard-chassis-power supply form factors for servers and workstations: ATX variations and the older Server AT form factor. Due to cooling and voltage considerations, Intel recommends the use of ATX form factor motherboards and chassis for the boxed Pentium III Xeon processor.

The ATX form factor simplifies assembly and upgrading of systems, while improving the consistency of airflow to the processor. With regard to thermal management, ATX power supplies draw air in to the chassis rather than venting out system air. Also, on an ATX motherboard, the processor slot is located close to the power supply, rather than close to the front panel of the chassis. Because of these differences the airflow in ATX chassis usually flows from the back of the chassis, directly across the processor and out of the front, side and rear vents of the chassis. Figure 2 shows proper airflow through an ATX system. For the boxed Pentium III Xeon processor, chassis that conform to the ATX Specification Rev. 2.01 are highly recommended. For more information on the ATX form factor, please visit the ATX Web site*. A list of ATX chassis manufacturers can also be found on the ATX Web site.

System Airflow Through an ATX Chasis (side view)

Figure 4: System Airflow Through an ATX Tower Chassis (side view)

Server AT form factor motherboards are not recommended because such designs are not standardized for effective thermal management. However, some chassis designed exclusively for Server AT form factor motherboards may yield efficient cooling.

As mentioned before, the newly introduced WTX specification was created to standardize a new motherboard and chassis form factor, fix the relative processor location, and allow for high volume airflow through a portion of the chassis where the processors are positioned. This allows for standard form factor motherboards and chassis to be used to integrate processors with more demanding thermal management requirements. Integrators are encouraged to use WTX form factor motherboards and chassis when they are available in late 1999. More information on the WTX specification can be found at the WTX Web site at*.

The following is a list of guidelines to be used when integrating a system.
  • Chassis vents must be functional and not excessive in quantity: Integrators should be careful not to select chassis that contain cosmetic vents only. Cosmetic vents are designed to look as if they allow air flow but little or no air flow actually exists. Chassis with excessive air vents should also be avoided. In this case, very little air flows over the processor and other components. In ATX chassis, I/O shields must be present. Otherwise, the I/O opening may provide for excessive venting.

  • Vents must be properly located: Systems must have properly located intake and exhaust vents.The best locations for air intakes allow air to enter the chassis and directly flow over the processor. Exhaust vents should be situated so that air flows on a path through the system, over various components, before exiting. Specific location of vents depends upon the chassis. For ATX systems, exhaust vents should be located both in the bottom front and bottom rear of the chassis. Also, for ATX systems, I/O shields must be present to allow the chassis to vent air as designed. Lack of an I/O shield may disrupt proper airflow or circulation within the chassis.

  • Power Supply Airflow Direction: It is important to choose a power supply that has a fan that draws air in the proper direction. For most ATX systems the power supply acts as an intake fan, drawing air into the system. Some power supplies have markings noting airflow direction.

  • Power Supply Fan Strength: PC power supplies contain a fan. In ATX power supplies, the fan draws air into the chassis. If exhaust vents are properly located, the power supply fan can draw enough air for most systems. For some chassis where the processor is running too warm, changing to a power supply with a stronger fan can greatly improve airflow.

  • Power Supply Venting: Most, if not all, air flows through the power supply unit, which can be a significant restriction if not well vented. Choose a power supply unit with large vents. Wire finger guards for the power supply fan offer much less airflow resistance than openings stamped into the sheet metal casing of the power supply unit.

  • System Fan - Should It Be Used? Some chassis may contain a system fan (in addition to the power supply fan) to facilitate airflow. A system fan is typically used with passive heatsinks. In some situations, a system fan improves system cooling. Thermal testing both with a system fan and without the fan will reveal which configuration is best for a specific chassis.

  • System Fan Airflow Direction: When using a system fan, ensure that it draws air in the same direction as the overall system airflow. For example, a system fan in an ATX system should act as an exhaust fan, pulling air from within the system out through the rear or front chassis vents.

  • Protect Against Hot Spots: A system may have a strong airflow, but still contain "hot spots." Hot spots are areas within the chassis that are significantly warmer than the rest of the chassis air. Improper positioning of the exhaust fan, adapter cards, cables or chassis brackets and subassemblies blocking the airflow within the system, can create such areas. To avoid hot spots, place exhaust fans as needed, reposition full-length adapter cards or use half-length cards, re-route and tie cables, and ensure space is provided around and over the processor.

Performing thermal testing
Differences in motherboards, power supplies, add-in peripherals and chassis all affect the operating temperature of systems and the processors that run them. Thermal testing is highly recommended when choosing a new supplier for motherboards or chassis, or when starting to use new products. Thermal testing can determine if a specific chassis-power supply-motherboard configuration provides adequate airflow for boxed Pentium III Xeon processors. To begin determining the best thermal solution for your Pentium III Xeon processor based systems, contact your motherboard vendor for chassis and fan configuration recommendations.

Thermal sensor and thermal reference byte
The Pentium III Xeon processor has unique system management capabilities. One of these is the ability to monitor the processor's core temperature relative to a known maximum setting. The processor's Thermal Sensor outputs the current processor temperature and can be addressed via the System Management Bus (SMBus). A "thermal byte" (8-bits) of information can be read from the Thermal Sensor at any time. The thermal byte granularity is 1°C. The reading from the thermal sensor is then compared to the Thermal Reference Byte.

The Thermal Reference Byte is also available via the Processor Information ROM on the SMBus. This 8-bit number is recorded when the processor is manufactured. The Thermal Reference Byte contains a pre programmed value that corresponds to the thermal sensor reading when the processor is stressed to its maximum thermal specification. Therefore, if the thermal byte reading from the Thermal Sensor ever exceeds the Thermal Reference Byte, the processor is running hotter than the specification allows.

Thermal testing can be done by stressing each of the processors in a fully configured system, reading the thermal sensor of each processor, and comparing it to the thermal reference byte of each processor to determine if it is running within thermal specifications. Software that can read information off the SMBus is needed to read both the Thermal Sensor and Thermal Reference Byte.

Thermal test procedure
The procedure for thermal testing is as follows:

Note If you are testing a system with a variable-speed system fan, you must run the test at the maximum operating room temperature you have specified for the system.
  1. To ensure maximum power consumption during the test, you must disable the system's automatic power-down modes or "green features." These features are controlled either within the system BIOS or by operating system drivers.

  2. Set up a method to record the room temperature, either with an accurate thermometer or thermocouple and thermal meter combination.

  3. Power up the workstation or server. If the system has been assembled properly, and the processor is properly installed and seated, the system boots into the intended operating system (OS).

  4. Invoke the thermally stressful application. (See the Thermally Stressful Applications section for more information.)

  5. Allow the program to run for 40 minutes. This allows the entire system to heat up and stabilize. Record the Thermal Sensor reading for each processor once every 5 minutes for the next 20 minutes. Record the room temperature at the end of the 1-hour period.
Warning Triangle After recording the room temperature, power the system down. Remove the chassis cover.

Allow the system to cool at least 15 minutes.

Using the highest of the four measurements taken from the thermal sensor, follow the procedure in the following section to verify the systems thermal management.

Calculation to verify a system's thermal management solution
This section explains how to determine whether a system can operate at the maximum operating temperature while keeping the processor within its maximum operating range. The result of this process shows whether the system airflow needs to be improved or the system's maximum operating temperature needs to be revised in order to produce a more reliable system. (An example is provided at the end of this section.)

The first step is to select a maximum operating room temperature for the system. A common value for systems where air conditioning is not available is 40°C. A common value for systems where air conditioning is available is 35°C. Choose a value that is right for your customer. Write this value on line A below.

Write the room temperature recorded after testing on line B below. Subtract line B from line A and write the result on line C. This difference compensates for the fact that the test was likely conducted in a room that is cooler than the system's maximum operating temperature.

(Appendix A contains a table for converting between Fahrenheit and Celsius scales.)
A. _ _ _ _ _ (Maximum operating temperature, typically 35° C or 40° C)
B. - ______ _ Room temperature ° C at end of test
C. _ _ _ _ _

Write the highest temperature recorded from the thermal meter on line D below. Copy the number from line C to line E below. Add line D and line E and write the sum on line F. This number represents the highest thermal sensor reading for the processor core when the system is used at its specified maximum operating room temperature running a similarly thermally stressful application. This value must remain below the Thermal Reference Byte value. Write the Thermal Reference Byte reading on line G.

D. _ _ _ _ _ Maximum reading from thermal sensor
E. + _______ Max. operating temperature adjustment from line C above
F. _ _ _ _ _ Max. thermal sensor reading in a worst case room ambient
G. _______ Thermal Reference Byte reading

Processors should not be run at temperatures higher than their maximum specified operating temperature or failures may occur. Boxed processors will remain within thermal specification if the Thermal Sensor reading is less than the Thermal Reference Byte at all times.

Processors should not be run at temperatures higher than their maximum specified operating temperature or failures may occur. Boxed processors will remain within thermal specification if the Thermal Sensor reading is less than the Thermal Reference Byte at all times.

If line F reveals that processor core exceeded its maximum temperature, then action is required. Either the system airflow must be significantly improved, or the system's maximum operating room temperature must be lowered. If the number on line F is less than or equal to Thermal Reference Byte, the system will keep the boxed processor within specification under similar thermally stressful conditions, even if the system is operated in its warmest environment.

To Summarize:

If the value on line F is greater than the Thermal Reference Byte, there are two options:
  • Improve system airflow to bring the processor's fan inlet temperature down (follow the recommendations made earlier). Then retest the system.

  • Choose a lower maximum operating room temperature for the system. Bear in mind the customer and the system's typical environment.
After implementing either option, you must re-calculate the thermal calculation to verify the solution.

Thermally stressful applications
Some commercially available software applications will cause the processor to heat up and dissipate more power through the heatsink and into the system. These thermally stressful applications can be used during thermal testing to help ensure that typical processing loads are accounted for in the thermal management of the system. Software programs will affect each microprocessor architecture uniquely (with respect to power dissipation). Some cursory verification of the system under test can determine which software program provides the highest temperature in the system. Using this application to test can provide assurance that applications being run on the platform will not cause the system to exceed the desired temperature operating range.

Future applications may demand more processor power and therefore generate more heat in the system. Adding additional thermal headroom for possible future applications can provide additional confidence in the system management of a server or workstation. This would mean verifying that the temperature measured during the thermal test was below the target specification by a certain value. A typical value to allow for thermal headroom may be 5°C or 10°C.

Below is a list of some applications and software conditions that operate on some common operating systems. These applications will affect different processors differently, but can cause most processors to dissipate a reasonable amount of power (and heat). Again, evaluating several applications on a system will show which applications cause the highest temperatures to be reached. It is highly recommended that several applications be used to determine the worst case thermal condition for the processor and that thermal testing be done with the worst case thermal application. Some applications require specific set up options or scripts to be in place for continual operation. Make sure that the application will operate in a thermally stressful fashion throughout the duration of the test.

For multithreaded operating systems, one instance of the software should be run for each processor in the system. Typically, the operating system assigns each successive instance of software to a unique processor.

Table 2. Example Applications That May Dissipate More Processor Heat1

Operating System Application Name Software Setup
DOS 6.22 Edit DOS with the file menu pulled down (Alt-F) and left pulled down
DOS 6.22 Quake* I ver 1.01
DOS 6.22 Heretic*  
Windows* 98 CPUMark32* Winbench98* suite
Windows 98 3D Winmark* Winmark98* suite
Windows* 98 SYSMark32* ver 1.0a BAPCO*
Windows 98 Idle Screen saver disabled, nothing running
Windows NT* 4.0 Prime95 ver 15.4.1
Windows NT 4.0 SPECint98* or SPECint95*  
Windows NT 4.0 SPECfp98* or SPECfp95*  
UnixWare* 2.01 Idle Waiting for user input at UNIX prompt
UnixWare* 2.01 145.fpppp (SPECfp95)  

  • Other brands and names are the property of their respective owners.

  • Evaluating several applications on a system will show which applications cause the highest temperatures to be reached.

Testing hints
Use the following hints to reduce the need for unnecessary thermal testing.
  1. When testing a system that supports more than one processor speed, test using the processor(s) that generates the most power. Processors that dissipate the most power will generate the most heat. By testing the warmest processor supported by the motherboard you can avoid additional testing with processors that generate less heat with the same motherboard and chassis configuration.

    Power dissipation varies with processor speed and silicon stepping. To ensure selection of the appropriate processor for your system thermal testing, refer to Table 1 for power dissipation numbers for boxed Pentium III Xeon processors. Boxed Pentium III Xeon processors are marked with a 5-digit test specification number, usually beginning with the letter S. Test specification numbers for a particular stepping of Pentium III Xeon processor can be found in the Pentium III Xeon processor table located in the Boxed Processor Test Specification Information document.

  2. Thermal checkout with a new motherboard is not necessary if all of the following conditions are met:
    • The new motherboard is used with a previously tested chassis that worked with a similar motherboard.
    • The previous test showed the configuration to provide adequate airflow.
    • The processor is located in approximately the same place on both motherboards.
    • A processor with the same or lower power dissipation will be used on the new motherboard.

  3. Most systems are upgraded (additional RAM, adapter cards, drives, etc.) sometime during their life. Integrators should test systems with some expansion cards installed in order to simulate a system that has been upgraded. A thermal management solution that works well in a system that is heavily loaded does not need to be re-tested for lightly loaded configurations.

Appendix A
The following table is provided to help convert degrees Fahrenheit to degrees Celsius.

Table 3. Fahrenheit to Celsius Conversions

° F ° C Notes ° F ° C Notes
59.0 15   118.4 48  
60.8 16   120.2 49  
62.6 17   122.0 50  
64.4 18   123.8 51  
66.2 19   125.6 52  
68.0 20   127.4 53  
69.8 21   129.2 54  
71.6 22 Note 1 131.0 55  
73.4 23   132.8 56  
75.2 24   134.6 57  
77.0 25   136.4 58  
78.8 26   138.2 59  
80.6 27   140.0 60  
82.4 28   141.8 61  
84.2 29   143.6 62  
86.0 30   145.4 63  
87.8 31   147.2 64  
89.6 32   149.0 65  
91.4 33   150.8 66  
93.2 34   152.6 67  
95.0 35 Note 2 154.4 68  
96.8 36   156.2 69  
98.6 37   158.0 70  
100.4 38   159.8 71  
102.2 39   161.6 72  
104.0 40 Note 3 163.4 73  
105.8 41   165.2 74  
107.6 42   167.0 75  
109.4 43   168.8 76  
111.2 44   170.6 77  
113.0 45   172.4 78  
114.8 46   174.2 79  
116.6 47   176.0 80  

  1. Typical office room temperature
  2. Typical maximum operating room temperature for a system in an air conditioned environment
  3. Typical maximum operating room temperature for a system in a non air conditioned environment.

This applies to:

Intel® Pentium® III Xeon® Processor

Solution ID: CS-007550
Last Modified: 25-Sep-2014
Date Created: 10-Dec-2003
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