All FB-DIMM modules have an Advanced Memory Buffer (AMB), which controls how information flows from module to module or to the memory controller. The first AMB provides a bi-directional interconnect to the memory controller on the motherboard and a different bi-directional interconnect to the next DIMM in the bank. The second FB-DIMM connects to the first DIMM and the next one in the chain. The AMB includes an on-board thermal sensor that provides a real-time AMB temperature to the memory controller. This allows the memory controller to monitor the AMB and invoke power throttling in extreme temperature conditions. Through power throttling, the memory controller may limit the DRAM bandwidth by slowing down memory accesses. The slower the bandwidth, the less power the DRAM consumes and temperatures decrease. The first test we did when it came to temperature testing was to install all of the Kingston 800MHz HyperX FB-DIMMs and monitor their temperatures using Everest 4.50. This is a fairly accurate look at the temperatures of the memory kits.
The AMB is the hottest part on the module as the thermal image above clearly shows. With temperatures reaching roughly 90C on the AMB it is clear why Kingston used a heat pipe to better cool this area.
Kingston used a single U-shaped heat pipe that makes direct contact with the AMB.
The first test we ran was to fill up all four banks with Kingston 800MHz HyperX FB-DIMMs at 2.0V with CL4 timings to observe their idle temperatures. The results showed that the outside FB-DIMMs were the coolest, which makes since as they got the most airflow. The modules averaged 66C, which is good, but that still seems high.
Just for fun, we placed a Corsair AIRFLOW memory cooling unit over the four FB-DIMM’s and the average temperature dropped by 11C down to 55C! That is a 17% decrease in temperature by simply adding a $19.99 fan. The Corsair AIRFLOW was designed for the taller DOMINATOR memory modules and just so happens to fit perfectly over the Kingston HyperX FB-DIMMs.
The final test was done using two traditional FB-DIMM modules in slots 1 & 2 with the HyperX modules in slots 3 & 4 with no fan. The inside modules are the ones that get the hottest and the difference between the two modules was night and day. The Micron FBDIMM with a Full Module Heat Spreader (FMHS) was found to run significantly hotter than the Kingston HyperX FB-DIMM with the dual-phased cooling system. This is proof positive that the Kingston modules run cooler. With the 12C difference between the inside modules it represents a temperature improvement of 18% over a traditional FB-DIMM module.