Note: On Mac Pro systems, the distribution of memory modules may affect the performance characteristics of your video applications.
*Final Cut Studio*: For best performance on Mac Pro install memory in risers symmetrically To achieve optimal performance when running Final Cut Studio applications, memory DIMM pairs should be installed evenly on both risers.
Note: DIMMs must be installed in pairs of equal size from the same vendor. For instance, you must not have one or three DIMMs on either riser at any time. Additionally, two DIMMs from different vendors should not be combined and used as a pair.
Other configurations of DIMM pairs are still compatible with Final Cut Studio, but may not achieve the same performance levels as when DIMM pairs are installed on both risers evenly.
For best performance on Mac Pro, install memory in risers symmetrically, DIMM pairs should be installed evenly on both risers.
DIMMs must be installed in pairs of equal size from the same vendor.
DIMMs from different vendors should not be combined and used as a pair. Other configurations of DIMM pairs are still compatible, but may not achieve the same performance levels as when DIMM pairs are installed on both risers evenly.
Solution This table shows Mac Pro RAM configurations that will achieve ideal performance when running Final Cut Studio applications:
http://docs.info.apple.com/article.html?artnum=304492
*Background Discussion:*
Memory is connected to the North Bridge via two 128-bit channels (256 bit). Each channel services two memory slots via the Advanced Memory Buffers (AMB) using FB-DIMMs. Every Mac Pro comes with two memory riser cards, each with four fully-buffered DIMM slots. With a total of eight DIMM slots available, you can install up to 16GB of memory. To help dissipate heat, every Apple DIMM you purchase for your Mac Pro comes with its own preinstalled heat sink. This unique heat sink lets fans run slower and quieter yet keeps the memory cool enough to run at full speed.
Mac Pro's memory architecture consists of two memory riser cards organized by branches, channels, and DIMMs. The memory controller hub (MCH) on the North Bridge has two branches with Branch 0 going to Riser A and Branch 1 to Riser B.
The North Bridge IC connects to an Advanced Memory Buffer (AMB) device on the FB-DIMM modules using a high speed serial link running at 4 GHz DDR, with 14 northbound (read) lanes and 10 southbound (write) lanes. The North Bridge IC has two high speed serial links, each capable of addressing four FB-DIMMs. The DIMMs are arranged in pairs operating in lock-stepped, dual channel mode to provide a 128-bit wide datapath, plus 16 bits of ECC.
Each memory riser card has four DIMM slots labeled 1 to 4.
On Riser A, Channel 0 serves DIMMs 1 and 3 and Channel 1 serves DIMMs 2 and 4.
On Riser B, Channel 2 serves DIMMs 1 and 3 and Channel 3 serves DIMMs 2 and 4.
The AMBs on DIMMs 1 and 2 connect to the MCH via a high speed serial bus. If installed, the AMBs on DIMMs 3 and 4 connect to the AMBs on DIMMs 1 and 2, respectively. The high speed serial bus consists of 14 unidirectional northbound lanes (towards the MCH) and 10 unidirectional southbound lanes (towards the DIMMs) to carry command, address, and data traffic.
The MCH operates each branch independently. At DDR2-667 speeds, each branch provides a peak theoretical thruput of 10.6 GBps of northbound (from memory to North Bridge) traffic and 5.3 GBps of southbound (from North Bridge to memory) traffic.
RAM Expansion: Developer Note
Further reading:
Tom's Hardware: Memory Bandwidth
