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| Page 1 of 1 | Author: kan
Date of review: 15-June-1998
Type Of Review: Articles/Editorials |
Introduction
What I am about to talk today is how to reduce the heat generated by your CPU.
There are two methods to do that :
- Install a good heat sink with fan and ensure proper ventilation of the casing
- Software method
What I will be touching on is the software method. In case you are not aware of, there are software available in the market like CPUIdle, Rain, Waterfall which make use of the HLT command to reduce the temperature of the CPU. The HLT command is a simple instruction that tells the CPU to 'sleep'. This way, it consumes less power and hence generate less heat.
The following text is taken from CPUIdle documentation :
Due to CMOS technology in which modern microprocessors are manufactured they do not only consist of transistors but also capacitors and resistors. The resistors create heat that must be conducted away from the processor. This is easier with higher temperature gradients. It is for that reason that microprocessors are not only equipped with large heat spreaders but also actively cooled with fans or Peltier cooling elements. Higher temperatures worsen parasitic effects like elektromigration or oxide breakdown that might eventually lead to failure. A temperature increase of 10 degrees centigrade means halfed lifetime for chips. This not only holds for the microprocessor but also for the voltage regulation module (VRM) that supplies the IO- and core voltages. Especially out-dated or cheap mainboard designs employ passive VRMs that generate additional heat in the PC.
Under normal circumstances the CPU isn't always active but spends much time waiting for the keyboard, harddisk or CD-ROM. What would be more logical than to turn off the CPU for that period? That's exactly what the HLT machine instruction (Opcode F4) does. Whenever the CPU encounters a HLT instruction the clock is halted and the CPU enters suspend mode until an interrupt, NMI or reset happens. With the advent of power saving microprocessors like the Cyrix Cx486S the instruction acquired an additional property. When "Suspend on HLT" is enabled in the configuration register the processor not only stops on HLT but also enters the power saving suspend mode.
Modern operating systems like Linux or Windows NT execute the HLT instruction in an idle priority thread. This thread is always executed when- as the name implies- the CPU is otherwise idle. Therefore no additional execution time is needed, the CPU will not run slower. This does not hurt performance since the CPU controls the powering-down of specific internal parts by hardware-control, so there's no software intervention needed for explicitly re-enabling a powered-down part (cited from set6x86 readme by Koen Gadeyne).
Using this feature the power consumption at the Windows NT prompt can be-according to German c't magazine- 2.1A (K6-166) to 5.3A (K6 233) lower than at the DOS prompt. With Intel processors the power saving is lower but also measurable. For Cyrix the "Suspend on HLT" feature must first be enabled if the BIOS does not provide support.
Windows 98 is suppose to have built-in HLT feature. But it was pulled out in the last minute. Don't ask me why.
So, does it really work? Yes, it does. We shall take a close look at CPUIdle 3.01.
The interface of CPUIdle is simple and clear. Installation is easy too. Just unzip the file into a directory, and run cpuidle.exe.
So, how do you really know it's working? For those people who are using the new motherboards like TX, LX or BX chipsets. You will have the following chips on your motherboard :
- LM75
- LM78
- LM79
- WinBond W83781D
These chipsets will provide vital information on your motherboard temperature, CPU temperature, voltages as well as fan RPM.
There is a software available called MotherBoard Monitor. What it does is to request information on your motherboard from the above chips.
Not only can MotherBoard Monitor display the values of your motherboard and CPU, you can also set your fans RPM thru the program. Notice that the program display Fan1, Fan2, Fan3 not available. This is because I am not drawing power from the motherboard, but instead drawing power directly from the Power Supply Unit (PSU). If you have those chasis fans, you should be able to see the Revolutions Per Minute (RPM) of the fan.
You can also set alarms to warn you when your temperature exceed a certain level as well as logging down of warnings into text or even HTML format.
Notice my motherboard temperature of 37ºC and CPU temperature of 43ºC ? This was recorded when CPUIdle is ACTIVE.
Now, take a look below without CPUIdle.
Notice that my CPU temperature rises to 59ºC (increases of 16ºC) and my motherboard temperature rises to 39ºC (increases of 2ºC). The CPU temperature rises quickly in less than a minute without CPUIdle!
So, if you are thinking of spending money getting a bigger, better heat sink, think again. Programs like CPUIdle really work. But of course, there are people who couldn't get the program to function properly.
Give it a try. CPUIdle and MotherBoard Monitor can be downloaded from our Utilities Section.
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