Creating "Fully Buffered Dual In Line Memory Modules" [FB-DIMMs] for the Mac Pro requires the developer to provide for thermal conditions other than those proposed in Intel's original reference design.
Mac Pro Air Flow for FB-DIMMs
The Mac Pro controls the air flow for FB-DIMMs and regulates the maximum permitted memory bandwidth to maintain a safe operating temperature for the FB-DIMMs.
To minimize acoustic noise and maximize memory bandwidth, FB-DIMMs are recommended to be equipped with sufficient thermal dissipation capabilities, to maintain a safe operating temperature on the FB-DIMM components, while with an air flow of 0.5 meters per second and at an ambient temperature of 25° C, during maximum memory bandwidth utilization.
The Mac Pro will ensure FB-DIMMs maintain a safe operating temperature by raising fan speeds to increase air flow, up to a maximum of 2 meters per second. If needed, the Mac Pro will also lower the maximum permitted memory bandwidth.
Note: To maintain a safe operating temperature at an ambient temperature of 35°C on FB-DIMMs using a JEDEC standard heat spreader requires an air-flow of approximately 3 to 6 meters per second. Therefore, designing adequate thermal dissipation capabilities on FB-DIMMs for the Mac Pro is strongly recommended to avoid raised fan speeds and lowered bandwidth during user operation.
Advanced Memory Buffer [AMB]
In order for the Mac Pro to maintain a safe operating temperature of the FB-DIMMs, the AMBs for each FB-DIMM must provide a functional temperature sensor.
Note: The Mac Pro will run the fans at full speed when detecting FB-DIMM's without a functional temperature sensor, which will maximize cooling on the FB-DIMM's. While the full speed of the fans maximizes the preservation of thermal integrity, FB-DIMMs with inadequate heat sinking may still overheat depending on ambient temperature and system load. In this case, the Mac Pro may shut down the system to protect the FB-DIMM from possible thermal damage.
Serial Presence Detect (SPD) personality byte
The personality bytes and other information not directly produced by the FB-DIMM developer should be provided by the AMB manufacturer.
There are several companies that have produced heat spreaders that meet the thermal conditions for the Mac Pro.
For more information contact firstname.lastname@example.org .
Apple Designed Heat spreader :
Apple has proposed the MO-256 FBDIMM Heatsink Option to the JEDEC FB-DIMM specification.
Document Revision History