HP Dx5150 - Compaq Business Desktop Configuration Manual page 4

There are four DIMM sockets on the system board, with two sockets per channel. The sockets are
labeled XMM1, XMM2, XMM3, and XMM4. Sockets XMM1 and XMM3 operate in memory
channel A. Sockets XMM2 and XMM4 operate in memory channel B.
The system will automatically operate in single channel mode or a higher-performing dual channel
mode, depending on how the DIMMs are installed.
If the user installs a pair of identical DIMMs in the same channel (slots 1 and 3), the system will
display a warning message during boot, suggesting that the 2 DIMMs should be in slots 1 and 2 for
optimum performance (dual channel).
"Identical" in this sense generally means that the DIMMs are the same size and have the same
number of memory chips on each side. If the user installs two DIMMs that are not identical in a dual-
channel pair of slots, then the system will display an error message stating that the memory is not in a
valid configuration.
Note that the first DIMM slot (XMM1), closest to the processor, must be populated for the system to
boot. If this is not done, the system will not boot, but the power LED on the front panel will blink red
5 times.
Figure 2. Valid Population Combinations
These are the 4 possible population combinations:
4