Memory in the Mac Pro is server-quality memory. In particular, it is ECC memory.
According to actual testing by barefeats.com (and an Apple tech note), full memory speed is not achieved unless 4 modules are installed correctly (“quad channel”). Please see “SPECIAL REPORT: What Everyone Should Know about Mac Pro Memory Upgrades” at barefeats.com for details.
According to barefeats.com, the speed gain ranges from nothing at all, to 25% faster on the 3.0 GHz model (slower CPU speeds will show less of a difference). Since the Mac pro is a rather expensive workstation suitable for users who need the performance, slowing its speed with inappropriate memory selection and/or installation is self-defeating.
The Mac Pro uses two memory “risers”. For quad-channel memory performance, the memory needs to be installed on both risers in pairs (eg 2 X 1GB on one riser and 2 X 1GB on the other riser, and in matching slots).
The following memory configurations (installed appropriately) allow peak speed:
- 4 X 512MB
- 8 X 512MB
- 4 X 1GB
- 4 X 1GB + 4 X 512MB
- 8 X 1GB
- 4 X 2GB
- 4 X 2GB + 4 X 512MB
- 4 X 2GB + 4 X 1GB
- 8 X 2GB
Note that the base memory configuration offered by Apple will not allow top performance:
- 1GB (2 X 512MB)
In other words, anything but the default 1GB setup is OK.