Test Setup

To test this heatsink out, I decided to compare it to my old Thermalright AX7. I would be using the same 80mm fan, which is a Blue Enermax 80mm Adjustable fan. For the test, the adjustable fan will be at full speed.

Here are all the specs for the test setup, that could possibly have an influence on temperatures:

• AMD Athlon XP 2100+ TBred B - 0248
• Gigabyte GA-7DXR
• 2x256 MB Crucial PC2100 DDR
• Retail Radeon 8500 64mb
• Enermax 350 Watt FMA PSU (with bottom 92mm fan)
• Modified Antec SX800 Case - 2 92mm & 1 80mm in front and 2 92mm in back - all Enermax Adjustable fans hooked to 4-port fanbus.
• Front fans have air filters
• Of course, the SLK 900U and AX7 with Arctic Silver II used for testing. Fans are installed exactly as you see above.

Before I begin the test, I want to point out how the 7DXR records the processor's temperature.

Yep, that's the temp probe. Something that makes the 7DXR very unique, is that the temp probe actually touches the bottom of the processor. I made sure of it too, by bending it up a bit more. This can result in pretty high temperatures, but the temps are more accurate than just measuring the temp of the "space" below the processor.

For the test, I wanted to see how each heatsink handled in each of the same conditions. Hence, the reason I used the same fan. I recorded temperatures in both Fahrenheit and Celsius, but ultimately decided to use Celsius as it is more universal.

Load was determined by running Folding at Home for 45 minutes - Average taken from Motherboard Monitor 5.3.3.0.

Idle was found by running the computer with no programs running and just basic background applications for 45 minutes - Average taken from Motherboard Monitor 5.3.3.0.

Room temperature was kept between 74-76 ºF for the endurance of the test.

Default Speed - 1.73 GHz @ 1.6v
Overclocked - 1.85 GHz @ 1.85v

Fans at High - CPU fan @ 3400 RPM (12v) / Case fans on High - System was fairly loud at this setting
Fans at Low - CPU Fan @ 2600 RPM (9.2v) / Case fans on Low - System was fairly silent at this setting

Results

As the graphs show, the SLK 900U performs exceptionally well, getting a lower temperature in all the tests. I was expecting lower temperatures, however. I think the main reason temps are a bit higher than expected is because the base wasn't as smooth as I'd hoped for. I put a thin layer of Arctic Silver II on the core. It wasn't until after the testing was complete that I realized that I probably should have put a thicker layer on to make up for the fairly deep machining marks on the base.

Something else to note is that I tried a 92mm Enermax adjustable fan and got close to the same temps as the 80mm fan. My only guess is that the huge amount of airflow (around 60cfm) was mostly blowing off the sides, because the fan is so large. I may try making a shroud in the future. However, there is a benefit from the air blowing off the sides, that air does help to cool surrounding components like your ram and capasitors.

Conclusion

Thermalright has never let me down. Now that I think about it, I have only ever owned Thermalright heatsinks. Starting with the SK6, then to the AX7, now to the SLK 900U. All those heatsinks have always performed incredibly well and this is just another example. Having been made of solid copper, it is quite heavy. However, you don't have to worry about this heatsink ever coming off since it's held through the motherboard. The design of the SLK 900U features the same design as all the other heatsinks in the SLK series, which creates very efficient cooling while allowing the air to move freely through the fins and out the bottom of the heatsink. With the 900U version being the largest in the SLK series, it offers more surface area and support for larger fans!

Other than the missing instructions, which can be found here, the whole package was as complete as can be. Including two mounting options for P4 users and featuring a very well thought out method for mounting through the motherboard, eliminating the annoyance of having to deal with bolts and nuts. Just screw the standoffs in with the right washers and you're set!

When it comes to getting the best heatsink, the SLK 900U shines, literally. If you want the best cooling for your AMD Athlon XP Processor, or Pentium 4 processor for that matter, the SLK 900U is what you're looking for. If the 900U seems to big or out of your league, for some reason, the SLK 800 is the best alternative. No matter what choice you make, going to Thermalright for your heatsink is the absolute best choice you can make!

Pros

• Ability to use a 92mm fan - finally, tons of air movement without the noise!!
• Easy installation using X-shaped piece of metal
• Screws through the motherboard - it isn't coming off
• Very efficient design
• 100% copper
• Looks spectacular
• Includes everything you need - and more!
• Two choices for mounting for Pentium 4 users
• The slender heatsink design allows air to help cool surrounding components

Cons

• Base has lots of machining marks
• Motherboard must be removed
• Very heavy - being careful is a must
• No instructions included

We would like to send a special thanks out to our friends at Thermalright for allowing us to review their top performer, the SLK 900U!