As I noted yesterday, the heat sinks on the SATech memory have greatly reduced surface area compared to that of the Apple modules. I downloaded Temperature Monitor to check out the temperature of the memory in my Mac Pro. I’m a bit concerned that the 2GB modules seems to be running very hot as compared with the 512MB modules. Do keep in mind that the 2GB modules are “dual rank” which means they have twice the chip count (chips on both sides of the module), and thus each chip has twice the memory density of the chips on the 512MB module, so greater heat should be expected. Or perhaps the chips are the same density, which would require 4 times as many chips—I’m not sure.
Shown below are the temperatures of the 8 modules (ambient temperature about 72° F). Modules A1/A2/B1/B2 are the 2GB modules, and A3/A4/B3/B4 are the 512MB modules.
Temperatures of the 8 FB-DIMMS
Fully stressing the machine, using diglloydTools to run all 4 cores at 100% and access 8GB of memory for 30 minutes or so results in a modest temperature rise of no more than 10° F, but that pushes the temperature close to 200° F at an ambient temperature of 81° F.
I want to emphasize that I’ve had no glitches with the memory, and the ECC memory status has never shown any errors. But memory bandwidth is apparently a concern in the Mac Pro if the modules are running too hot—see Apple Tech Note Thermal Considerations for Mac Pro FB-DIMMS.
I asked SATech.com to investigate the temperature issue for me. They responded:
The memory module temperatures will be definitely higher than the 512mb due to the density. 2gb FB DIMMS are designed to work in a server environment only, so the heat spreaders are designed to work in that environment. The heat spreaders on these modules are Jedec compliant and the modules are Super Micro and Mac certified means tested under extreme operating conditions. So no cause to worry even if the outside temp increases.
A reader requested pictures and several are shown below. Click for larger images.
Mac Pro riser board, fully populated with four FB-DIMMS
Slots 3 and 4 (top) contain Apple 512MB modules
Slots 1 and 2 (bottom) contain 2GB SATech modules
Apple 512MB FB-DIMM [side view]