How to Correctly Assemble PCs with Pentium 4 Prescott
By Daniel Barros on March 16, 2005


Introduction

Pentium 4 processors with the Prescott core have new specs for case, cooling and power supply. A lot of people without this knowledge is facing overheating problems, slowness on their PC or even getting their power supply burned out. Learn in this tutorial how to correct assemble PCs based on the Pentium 4 with Prescott core.

With the release of the Pentium 4 processor based on the Prescott core Intel was able to keep ahead of competition: 90 nanometers (0.09 micron) technology, higher clocks, SSE3 technology and 1 MB L2 memory cache. On the other hand, this new processor dissipates a lot more heat than the previous Pentium 4 based on the Northwood core, and it demands adequated casing (different case type from the previous Pentium 4 processors) and also that you know the real power rating of your power supply.

Intel was very shy in informing the new requirements on how to correctly integrate CPUs with Prescott core. People that buy the boxed processor get a brochure in several languages informing that you must visit http://www.Intel.com/go/chassis to get all thermal specs demanded for the processor, and is also advised that in order to work correctly, the temperature inside the computer case shall not be over 100.4 F (38 C).

The problem is that not so many people care to read this brochure and people that buy the OEM model (i.e., outside the box) don't get any instruction about the new thermal and power requirements for Precott, and in just a few months after the Prescott release a lot of PCs started to show up on maintenance services. Slow PCs caused by the Thermal Throttling feature (click here to learn more about this feature), which protects the processor in case of overheating preventing it from burning, overheating and even burned power supplies are the most common symptoms of PCs wrongly assembled.

Of course the largest manufacturers and largest integrators didn't have any problem at all, but small integrators and do-it-yourself users are facing a lot of overheating problems with the new Prescott CPU.

Casing Requirements

At http://www.intel.com/cd/channel/reseller/asmo-na/eng/53211.htm Intel gives all the specs for correctly integrating CPUs with Prescott core (Pentium 4 and Celeron D). Let's talk about the case requirements.

Regular cases usually keep the temperature inside the PC between 104 F and 113 F (40 C and 45 C) with an ambient temperature of 95 F (35 C). In the Prescott specs, Intel asks to keep the temperature inside the case only five degrees Fahrenheit (three degrees Celsius) above the ambient temperature, which must be up to 95 F (35 C).

So, the main casing requirement is to keep the temperature inside the PC below 100 C (38 C). The case may not follow the design specs from Intel, but it must be capable of keeping the PC inner temperature below 100 C (38 C).

In order to achieve the required temperatures, Intel released its Chassis Air Guide Design 1.0, which uses a case with a 60 mm duct on one of its side, adjustable to correctly fit the processor, pulling fresh air from outside the case.

Prescott Air Flow

Figure 1: Correct case airflow, according to Intel.

 

Prescott duct

Figure 2: Correct distance between the air duct and the CPU cooler.

In order to make the air enter the duct and cool down the CPU, it is necessary to have an 80 mm fan installed on the back of the case, pulling hot air from inside the case to the outside. The duct must be installed between 1/2" and 13/16" (12 and 20 mm) away from the CPU cooler to work (see Figure 2).

Prescott 80mm extra fan

Figure 3: 80 mm fan for removing the hot air from inside the computer.

These recommendations are for low cost PCs based on the Celeron D processors.

For more advanced systems using the Pentium 4 CPU and more powerfull video cards, Intel noticed that the above specifications were not enough, so they released the Chassis Air Guide Design 1.1, which increases the side duct to 80 mm, the rear fan to 92 mm and also added a side window on the case above the motherboard slots, in order to cool down the system daughterboards (see Figure 4).

Pentium 4 Prescott Case
Figure 5: Chassis Design Guide version 1.1 adds a side window and increases the side duct to 80 mm.

Power Supply Requirements

First of all: forget generic power supplies! The current requirements for systems based on Prescott CPUs are far greater than previous Intel processors. The power supply must be capable of providing at least 16 A at its 12 V output and no generic power supply can provide this current. Usually generic 400 W power supplies are capable of giving 12 A at its 12 V output, at most. Using a generic power supply with Prescott processors can burn outr the power supply in just a few months, risking all the system.

Generic Power Supply

Figure 5: A 400 W generic power supply, innadequated to Prescott processors (this particular model can only supply 10 A at its 12 V output).

Seventeam ST-350BKV power supply
Figure 6: Seventeam ST-350BKV power supply, which is adequated to Prescott processors (it can supply up to 18 A at its 12 V output).

Another issue is that generic power supplies can bring wrong information on their labels. We found the same power supply we show in Figure 5 with a different label stating that it can provide 14 A at its 12 V output. So, it is hard to believe on the generic power supplies labels!

Thus it is adviced to use a power supply with at least 250 W true power from a known brand like Seasonic, Seventeam, Zalman, Emacs, Enermax, OCZ, etc.

For systems with high-end video card and several hard disks it is good to think on power supplies with 400 W true power or more.

At http://www.intel.com/cd/channel/reseller/asmo-na/eng/tech_reference/35815.htm you will find Intel list of tested and approved power supplies for Prescott-based systems.

Our Tests

In order to test how the side duct and the rear fan interfere on the inner temperature of systems based on the Pentium 4 Prescott, we conducted three tests: system assembled with a tower case with side duct, side window (grating allowing air to flow above the motherboard slots) and rear fan; same system with the rear fan turned off; same system with the side duct removed and its hole closed, the side window closed and the rear fan turned off.

The test consisted in measuring two temperatures, processor and "system zone" (area were the MOSFET transistors of the voltage regulator are located), with the case closed, first with the computer turned on but doing nothing and then with the CPU working at 100% of its processing power.

We used an Intel D865GVHZ (P22 BIOS) motherboard together with a Pentium 4 Prescott 2.8 GHz with external frequency of 533 MHz, without Hyper-Threading technology, using the cooler and thermal paste that came with the CPU ("in-a-box" model) and a Seventeam ST-350BKV power supply, all assembled on a Casetek BP-1005 case, which satisfies Intel's requirements for Prescott CPUs.

Testing Equipment

Figure 7: Equipment used on our tests.

 

Casetek BP-1005 case

Figure 8: Casetek BP-1005 case.

We measured the temperatures using Intel Active Monitor v1.2.1 program. The testing procedure was to put our CPU running at 100% of its processing capacity using the program CPUBurn v1.4 for 10 minutes. Then we monitored the CPU and "system zone" temperatures for 5 minutes and recorded the average temperatures, measured throught the motherboard thermal diodes. After this process we reduced the CPU usage near 0 %. After 30 minutes we checked if the CPU temperature has stabilized and we started monitoring the CPU and "system zone" temperatures again for five minutes. We also used Throttle Watch program (read our tutorial on this subject) to check if the Thermal Throttling feature was being turned on or not during our tests. The room temperature during our tests was 82 F (28 C).

Results

You can check the results from our tests on the tables below.

Idle CPU
  (1) (2) (3)
Processor 122 F (50 C) 127.4 F (53 C) 127.4 F (53 C)
System Zone 98.6 F (37 C) 104 F (40 C) 105.8 F (41 C)

CPU at 100%
  (1) (2) (3)
Processor 152.6 F (67 C) 154.4 F (68 C) 158 F (70 C)
System Zone 111.2 F (44 C) 116.6 F (47 C) 122 F (50 C)

Legend:

(1) With side duct and side window opened and rear fan turned on.
(2) With side duct and side window opened and rear fan turned off.
(3) With side duct and side window closed and rear fan turned off.

With adequated casing and cooling everything was between the specs, even with the high temperatures achieved.

Without the rear fan the temperature increased 5 F (3 C) while the CPU was idle comparing the results obtained with the rear fan turned on. When the CPU load was at 100% the temperature increased only 2 F (1 C) when we turned the rear fan off, but this small difference only occured because we were using a power supply with very good cooling system (120 mm fan that change its speed depending on the power supply temperature). If we used a regular power supply certanly the results would be worse.

On our third test we simulated our system installed on an innadequated case. We removed the side duct and closed its hole and the side window with paper and tape (see Figure 9).

Duct closed


Figure 9: We closed all side holes from the case.

Without the side duct and with the rear fan turned off, the system heated a lot and on the very first minutes of testing with the CPU at 100% processing load the Intel Active Monitor alarm started beeping, indicating that both processor and system zone programmed temperatures alarm were reached (122 F/50 C for system zone and 156 F/69 C for CPU). As for the system zone, Intel recommends to increased the default alarm temperature from 122 F (50 C) to 140 F (60 C). As for the CPU temperature, the results were disturbing: only 7 F (4 C) below the trigger when the Thermal Throttling overheating protection comes in action. During this condition the power supply fan was spinning at 2,000 rpm trying to keep the system temperature as cool as possible and the air that came out of the case was very hot. A computer working in a situation like this would have problems for sure, as the high inner temperature also affects other components like hard disks.

Conclusion

This test proved that Pentium 4 processors based on the Prescott core really need special care when integrating a system with them. A good case with side duct and rear fan and a power supply with a true power of at leat 250 W are minimal requirements for a system based on these processors, or you will face several problems in just a few months due to overheating.

Our test served also to show us how the original cooler that comes with the CPU isn't adequated in some situations, showing that it is operating "at the edge". The CPU almost reached its maximum operating temperature of 165 F (74 C), even when the rear fan and the side duct were present.

Keep in mind that our tests were performed with a very simple office configuration, using a CPU that is not high-end, integrated video and a very good power supply. Imagine if we were using a high-end CPU, a high-end VGA which produces a lot of heat inside the case  and a generic power supply!

Also remember that our room temperature was of 82 F (28 C). Depending on the city you live, the situation would be critical. It is very likely that with a higher room temperature the system would activate its Thermal Throttling feature to keep the CPU temperature down.

Some can say that running the CPU at 100% load for long period of times as an artificial scenario and this situation rarelly occurs on daily computer use. This is not true. Nowaday the latest games keep the CPU load at 100% for very long periods of time. Imagine this system running at a LAN party!

If you want to assemble a PC using the Pentium 4 Prescott, buy the best power supply and best case you can. It is also recommended to change the original cooler for a better one. If you buy a PC already assembled, check if the PC was assembled using Intel's guidelines. This way you will avoid future headaches.

Originally at http://www.hardwaresecrets.com/article/How-to-Correctly-Assemble-PCs-with-Pentium-4-Prescott/106


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