Review: Thermalright SLK-900U Heatsink

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February 20, 2003 by Mike Chin

Product Thermalright SLK-900 U Heatsink
Supplier Silicon Valley Compucycle (SVC)
Market Price US$55

The Thermaright SLK-900U has been available only for a few scant weeks, and it is already developing a mystique as the new King of Coolers. It is shown above along side a 1" tall fan mounting grommet for scale. Yes, it is a big one.

Specifications from Thermaright:


  • L99 x W59 x H45 (mm) Top, without fan
  • L67 x W81 x H45 (mm) Bottom, without fan


  • 570g (heat sink only; for AMD)
  • 587g (heat sink only; for Intel)
  • A 92x38mm fan adds ~180g; a fan this size is a standard option that Thermalright supplies. A 92x25mm weighs ~100g; a 80x25mm fan weighs ~80g.

Review samples are hard to come by as demand is high, but online retailer Silicon Valley Compucycle (SVC) was able to help us with one from their very first batch. SVC currently has the unit priced at US$49.99.

The SLK-900U should look familiar: it is essentially an enlarged SLK-800 (shown on the right in these comparative photos) with a modified mounting system to accomodate both P4 and socket-A processors. The "U" stands for universal. It has the same basic structure as the 800, a U-shaped tunnel through which a clip runs, and to which the fins are soldered. It has the same number of fins spaced fractionally farther apart, so that its overall width is a tiny bit bigger.

The weight as not that much greater than the SLK-800: 587 grams (in P4 form) versus 505 . But adding a 92x25mm fan does put it up to nearly 700 grams, which is getting up there. It's still substantially lighter than the imposing 898 gram Zalman 6500B-CU, which is its natural main competitor among P4 heatsinks; till now, the Zalman has held the P4 cooler crown here at SilentPCReview.

The fins are shaped in such a way as to provide stepped notches that are perfect fits for 70mm, 80mm and 90mm fans. It is a tiny bit shorter, its fins some 3/8" longer -- this additional length is what allows the SLK-900 to accomodate a 92mm fan. The SLK-800 only handles up to an 80mm fan. The longer fins also make for a larger cooling surface area. I would guesstimate it to be at least 15% larger.

The SLK-900U comes in the usual nice sturdy brown cardboard box Thermalright uses for all its products (at least the ones I've seen). There is a large assortment of bits and pieces:

  • Wire clips for mounting different diameter / thickness fans.
  • Adaptor flanges and clips for use with the standard mounting frame on P4-478 motherboards.
  • Through-the-motherboard mounting anchors and hardware with a steel reinforcing backing plate (shown below) that can be used with either P4 or Socket-A. This is the only way it can be used it with Socket-A; it is a good option for the P4 as well, given the high mass of the heatsink, especially in conjunction with a 92 x 38mm fan. The plate has a square hard rubber pad in the center to insulate it from the motherboard PCB traces. The combination of bolts and the steel reinforcing plate results in a very secure mount that is second to none. Even ground shipping of a PC installed with this HS should pose no serious danger.

As delivered, the SLK-900 is ready for use in a Socket-A motherboard. To use it with a P4, steel flanges have to be screwed on, as shown in the photo below. This allows the use of the conventional quick mount clips or the through-the-board spring-loaded bolt mounting (much like Alpha and Swiftech).

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