Hardware reference guide

Hardware Upgrades
The following processor bus frequencies are required for the system to run at the
supported memory frequencies.
Memory Frequency Required Processor Bus Frequency
266 MHz 400 MHz, 533 MHz, or 800 MHz
333 MHz 533 MHz or 800 MHz
400 MHz 800 MHz
If a memory frequency is paired with an unsupported processor bus frequency, the
system will run at the highest supported memory speed. For example, if a 333 MHz
DIMM is paired with a 400 MHz processor bus, the system will run at 266 MHz, the
highest supported memory speed.
The system will not start if you install unsupported DIMMs.
DIMM Sockets
The system will automatically operate in single channel mode or a higher-performing
dual channel mode, depending on how the DIMMs are installed.
In single channel mode, the maximum operational speed is determined by the
slowest DIMM in the system. For example, if the system is populated with a
DIMM that is 266 MHz and a second DIMM that is 333 MHz, the system will
run at the slower of the two speeds.
In dual channel mode, all DIMMs must be identically matched. DIMMs in the
DMM1 and XMM3 black sockets must be identical; DIMMs in the XMM2 and
XMM4 blue sockets must also be identical. Therefore, if you have one
preinstalled DIMM in socket XMM1 and are adding a second DIMM, it is
recommened that you preinstalled DIMM in socket XMM1 and are adding a
second DIMM, it is recommened that you install an identical DIMM into the
XMM3 socket. If you are populating all four DIMM sockets, use identical
DIMMs in each socket. Otherwise, the system will not operate in dual channel
mode.
2-8 Hardware Reference Guide