Thermalright SLK-948U

A very good heatsink for P4 and Athlon64FX CPUs – Joe

SUMMARY: A very good heatsink for P4 and Athlon64FX CPUs.


Size: L95 x W64 x H45 mm (fins only, no fan); Weight: 635 grams.

The good guys at Thermalright were nice enough to send us a sample of Thermalright’s SLK-948U. This is the usual all-copper construction we’ve seen from Thermalright, designed for both P4 and Athlon64FX use.

The base is a copper baseplate:


I could feel very slight ridges as I dragged my fingernail over it.

The 948U ships with a LOTS of parts:


There are mounts to use Intel’s retention bracket and spring-loaded bolts for both P4 and Athlon64FX motherboard mounting. Fan clips are included for 60, 80 and 92 mm units. Included is an instruction sheet which details what goes where for which CPU.

Overall, the build quality is very good.


The SLK-948U was tested on the CPU Die Simulator which gives results that are unaffected by motherboard influences. For testing, I used a Delta FFB0812EHE, 80 cfm @ 5700rpm, 52.5 dBA¹, at 69.7 watts; this fan features vanes in the base which straighten airflow into the heatsink. I varied rpms to give a range so users can match performance to noise tolerance.


Die Temp
Ambient Temp
SLK-948U, 5515 rpm, 74 dBA¹
40.8 C
23.5 C
17.3 C
SLK-948U, 4500 rpm, 67 dBA¹
41.1 C
22.6 C
18.5 C
SLK-948U, 3510 rpm, 62 dBA¹
42.5 C
22.6 C
19.9 C
SLK-948U, 2516 rpm, <50 dBA¹
44.7 C
22.0 C
22.7 C

Delta = CPU temp – Ambient Temp
C/W = Delta / CPU Watts

Interpreting C/W: For every watt (CPUw) that the CPU
consumes, the HSF will limit the CPU’s temperature rise to (C/W x CPUw)
plus the temperature at the HSF’s fan inlet. For example, at an ambient temp of 25 C, a C/W of 0.25 with a CPU radiating 50 watts means that CPU temp will increase 50 x 0.25 = 12.5 C over ambient temp, or 37.5 C. The lower the C/W, the better.

Test results place the Thermalright SLK-948U in the upper rank of heatsinks (Heatsink Ranking) tested to date.


Performance, as usual, is dependent upon how much noise you’re willing to tolerate. Thermalright’s SLK-948U is a heatsink for P4 and Athlon64FX CPUs. Featuring myriad mounting hardware, it could be a heatsink that will live through some upgrades and CPU switches.

Thanks again to Thermalright for sending this our way. The SLK-948U is available at The Heatsink Factory.

¹Note that manufacturers measure fan noise usually 3 feet from the fan.

Email Joe