I'm curious who makes the memory you use in your Mac Pro -- both the stock Apple memory and any third party memory you've added. But first, is there a tool that tells you this already? If not, here's how I've done it for my machine. Run System Profiler (in /Application/Utilities). Under Hardware, select Memory. For each DIMM you have installed, post whether it was pre-installed "Apple" RAM or where you ordered it from and what "brand" they claimed it was. Then, from System Profiler, include: Manufacturer Whether or not the serial number changes (for FB-DIMMs that are the same part number) Here's my data: A1/A2/B1/B2: 2GB FB-DIMM from MacRamDirect (their house "HyperVelocity" brand) Manufacturer: 0x014F Serial number does NOT change when selecting any of these 4 slots A3/B3: 1GB FB-DIMM (original Apple RAM that shipped with my machine) Manufacturer: 0x802C Serial number DOES change when selecting these 2 slots A4/B4: 1GB FB-DIMM from MacRamDirect (supposedly the same "Samsung" memory used by Apple. The MacRamDirect label says "Samsung") Manufacturer: 0x014F Serial number does NOT change when selecting these 2 slots JEDEC publication number JEP-106-X provides manufacturing identification codes. 0x014F is in bank 2 and is assigned to Transcend Information. 0x802C is in bank 1 (the high bit is a parity bit) and indicates Micron Technology. (I can look up others as they are posted.) It appears Apple used Micron memory in my Mac Pro (the sticker on the FB-DIMMs had the Micron logo and I assume they use their own DDR2 chips) which makes me wonder why MacRamDirect says Apple uses Samsung? I do realize that the manufacturing code on the FB-DIMM SPD is not necessarily indicative of who makes the actual memory chips on the FB-DIMM, but it's still an interesting exercise nonetheless. The reason I am curious about whether or not the serial number changes for your RAM is because according to JEDEC Standard 21-C Page 22.214.171.124, Appendix X: Serial Presence Detect for Fully-Buffered DIMM (Revision 1.1) it clearly says (emphasis mine): The supplier must include a unique serial number for the module. The supplier may use whatever decode method desired to maintain a unique serial number for each module. One method of achieving this is by assigning a byte in the field from 122-125 as a tester ID byte and using the remaining bytes as a sequential serial number. Bytes 117-125 will then result in a nine-byte unique module identifier. Note that part number is not included in this identifier: the supplier may not give the same value for Bytes 119:125 to more than one DIMM even if the DIMMs have different part numbers. so it appears the Transcend modules I got from MacRamDirect violate this requirement.