I have a 2009 Mac Pro with dual 2.66GHz Xeon’s. They are X5550 chips. The computer has 24GB of 1333MHz ram in it, yet the computer will only address it as 1066. I’m wondering if anyone has experienced this (in Windows or OSX machines) and if so, what they did to address it.
Al is correct; you must contact Apple. The BIOS is responsible for all memory-related settings and initialization. Their BIOS may not have support for 1333MHz base clock.