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The objective of these tests is quite simple.  Determine which CPU cooler program will keep my processor running its coolest while adversely affecting performance the least. I have assembled a group of temperature and performance readings for real-world applications and synthetic benchmarks. What I have found is that while all of the programs help to keep the CPU from running as warm, some of the versions of CPUIdle don't seem to be very effective in keeping the processor cool during file transfers.

The Cooler Programs
How do these programs work?  Basically by executing an "HLT" instruction to the processor to put itself into a suspend mode when it is not actively computing.  Windows NT and many non-MS operating systems do this as a normal procedure.  Windows 95 and Windows 98 do not.  The HLT instructions offer the benefit of less power consumption when the CPU is idle and no benefit when the CPU is actively processing.  However, many tasks do not require the CPU to be computing constantly and this is when these programs go to work.

The methods of enabling the suspend mode differ between CpuIdle and Waterfall/Rain.  CpuIdle uses a virtual device driver (VxD) and Waterfall and Rain do not. (The latest versions of CPUIdle use either depending of the mode you choose.)  With all three programs, the instructions are carried out in the Ring0 level of the processor's architecture.  Ring0 is the most privileged ring of the architecture.  While the majority of people using these programs are not experiencing problems, it is quite possible for programs written to run in this privileged ring to adversely affect how other programs run.

There have been reports of different problems associated with each of these programs, ranging from locked up computers (infrequent) to static coming through the system speakers (not uncommon).  Personally, I have not experienced any of these situations over the last year of use.  For the most recent reports of problems, I find that searching DejaNews with "cooler program name problems" yields a good amount of reading material.  Because it has been available longer, there is more documented information for the various versions of CpuIdle.

Taking Temperatures
First I needed a way to monitor the CPU's temperature.  As my motherboards do not include this function, I needed to add some type of thermometer to my system.  I have ended up with a quite an assortment of thermometers to take care of this task, including a Radio Shack Temperature Sensor and Control Module, 2 Radio Shack Indoor / Outdoor Thermometers, and a very accurate Omega model HH22 Digital Thermocouple Thermometer using a type K thermocouples  (Thanks Charlie!). More information on the thermometers I use and how they have been modified can be found by clicking on the highlighted links.The processor temperatures are taken from the metal slug of the Celeron A and from the rear of the CPU for the AMD K6.  Heat sink temps are taken from thermistors  located as close to the center of the heat sink as possible.  Case temp for the BH6 is  taken next to the LM79  monitoring chip.  Case temp for the AMD is taken from the highest point of the board inthe case.  Room temp is taken from about 2 feet higher than the level of the case. System  Configuration
Abit BH6 board FL BIOS
Intel Celeron 300A (MALAY-98 330 740 - SL2WM) O/C'd to 464 @ 2.1v
CPU Cooler PII dual fan and Aavid Celeron heat sink (sandwiched)
(1) 64 MB PC100 RAM (HM5264 805TTB60 Hitachi)
Quantum Fireball SE 3.2
Quantum Fireball ST 3.2
Matshita CR-574 CD ROM
Matrox Millennium II G200 8 MB AGP
DCS S805 A3D Sound Card
D-Link DE-528 Ethernet Card
Hayes 5675 56K v.90 / Flex Modem
Inwin A500 Case w/ cooling modifications
Win95 OSR2

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