Apple Memory Module 2GB 667MHz DDR2 FB DIMM ECC - 2x1GB
For maximum performance, Mac Pro uses 667MHz DDR2 fully buffered ECC memory, a new industry-standard memory technology that allows for more memory capacity, higher speeds, and better reliability. When using all four memory channels, Mac Pro has a 256-bit wide memory path for a maximum memory bandwidth of 21.3GB per second. To achieve maximum bandwidth, four or more DIMMs should be installed in a Mac Pro.
Please note: The fully buffered DIMMs made by Apple include a unique heat sink that provides more efficient cooling than other FB-DIMMs. These FB-DIMMs require less airflow to stay cool and allow the internal fans to spin at slower speeds, improving system acoustics. FB-DIMMs made by other manufacturers that do not include a sufficient heat sink may cause the fans to run faster (and louder) or the memory chips to run slower so as not to overheat.