Intel® Pentium® II Xeon® Processor
Thermal Management

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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 Intel® Pentium® II Xeon™ processors.

It is assumed that the reader has a general knowledge of and experience with workstation and server operation, integration, and thermal management.

Thermal management

All systems using Pentium II Xeon processors require thermal management. In this case, "thermal management" includes two major elements: (1) a heatsink properly mounted to the processor and (2) effective airflow through the system 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 II 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.

Proper thermal management is achieved when heat is transferred from the processor to the system air, which is then vented out of the system. Boxed Pentium II Xeon processors are shipped with an attached passive heatsink, which requires system airflow to effectively transfer processor heat to the system air. It is the responsibility of the system integrator to ensure adequate system airflow.

This document makes recommendations for achieving good system airflow.

Integrated heatsink

Boxed Pentium II Xeon processors are shipped with an attached heatsink. The processor and heatsink should be used following the directions contained within the boxed Pentium II Xeon processor installation notes. Figure 1 shows the processor and heatsink.


Figure 1. Boxed Pentium® II Xeon® Processor and Heatsink

The heatsink that ships with the boxed Pentium II Xeon processor has already been securely attached to the processor. A small amount of thermal grease (already applied) provides effective heat transfer from the processor to the heatsink. The heatsink requires sufficient system airflow in order to keep the processor cool.

Some retention mechanisms supplied with Pentium II Xeon processor based motherboards provide locations for mounting small fans that draw air through the heatsink's cooling fins. Figure 2 shows an example of a second Pentium II Xeon processor being installed in a dual retention mechanism (DRM). In this example, two small fans are installed in the DRM. The fans ensure airflow over the cooling fins of the second processor's heatsink. Note that, unlike the second processor, the first processor has no fans directly drawing air across its heatsink. The system must provide adequate airflow to cool the first processor, which is without its own fan. The DRM fans must draw hot air from both processors out of the chassis. Check with your motherboard manufacturer for details about retention mechanisms and cooling solutions.

dual retention mechanism

Figure 2. Boxed Pentium® II Xeon™ Processor Being Installed into Dual Retention Mechanism (DRM)

System airflow

System airflow is determined by:

  • Chassis design
  • Chassis size
  • Location of chassis air intake and exhaust vents
  • Power supply fan capacity and venting
  • Location of processor(s) slots
  • Placement of add-in cards and cables

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

The ATX form factor simplifies assembly and upgrading of PCs, while improving the consistency of airflow to the processor. On ATX motherboards, the processor slot is located close to the power supply, rather than to the front panel of the chassis. This increases air circulation flowing directly across the processor. System component heat is dissipated into the chassis environment that is exhausted out while fresh air is brought in. Figure 3 below shows an example of typical airflow through an ATX system. Intel recommends ATX chassis that comply with the ATX 2.01 specification found on the ATX Web site . The ATX Web site also lists chassis manufacturers.


Figure 3. System Airflow through ATX Tower Chassis (side view)

The following is a list of guidelines to be used when integrating a system.

  • Provide sufficient air vents: Systems must have adequate air vents in addition to a fan. Chassis vents must be fully functional. System builders should be careful not to select chassis that contain cosmetic vents only. Proper location of vents results in a good stream of air flowing over the processor.

  • Power supply air flow direction: It is important to choose a power supply with a fan that moves air in the proper direction. For most ATX systems, the power supply acts as an intake fan, pushing air out of the system.

  • Power supply fan strength: For some chassis that are running too warm, changing to a power supply with a stronger fan can greatly improve airflow.

  • System fan--should it be used? Some chassis may contain a system fan to assist airflow. A system fan is typically used with passive heatsinks. In some situations, a system fan greatly 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 moves air in the same direction as the overall system airflow. A system fan in an ATX system should act as an exhaust fan, moving additional system air out through the exhaust vents in the chassis.

  • 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. Such areas can be created by improper positioning of the exhaust fan, adapter cards, cables, or chassis brackets and subassemblies blocking the airflow within the system. 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.
Thermal testing (system checkout)

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 II Xeon processors. To begin determining the best thermal solution for your Pentium II Xeon processor based systems, contact your motherboard vendor for chassis and fan configuration recommendations.

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 II Xeon processors. Boxed Pentium II 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 II Xeon processor can be found in the Pentium® II Xeon® Processor Specification Update, Order No. 243776.

    Table 1. Boxed Pentium® II Xeon® Processor Information

    Processor Core Speed (MHz) and L2 Cache Size Boxed Pentium® II Xeon® Processor Stepping Maximum Thermal Plate Temp (°C) Power Dissipation (W)
    400/512KB B0/B1 75 30.8
    400/1MB B0/B1 75 38.1
    450/512KB B1 75 34.5
    450/1 MB B1 75 42.8
    450/2 MB B1 75 46.7

  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.

    This applies to:

    Intel® Pentium® II Xeon® Processor

    Solution ID: CS-011195
    Last Modified: 06-Oct-2014
    Date Created: 14-May-2004
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