Single- And Dual-Rank Dimms; Dimm Numbering - HP ProLiant BL45p User Manual

For optimal performance in most applications, populate memory bank 1 for
every populated processor socket.
DIMM banks are active only when the corresponding processor socket is
populated.

Single- and dual-rank DIMMs

PC3200 DIMMs can either be single- or dual-rank. While it is not normally
important for you to differentiate between these two types of DIMMs, certain
DIMM configuration requirements are based on these classifications.
Certain configuration requirements exist with single- and dual-rank DIMMs that
allow the architecture to optimize performance. A dual-rank DIMM is similar to
having two separate DIMMs on the same module. Although only a single DIMM
module, a dual-rank DIMM acts as if it were two separate DIMMs. The primary
reason for the existence of dual-rank DIMMs is to provide the largest capacity
DIMM given the current DIMM technology. If the maximum DIMM technology
allows for creating 2-GB single-rank DIMMs, a dual-rank DIMM using the same
technology would be 4-GB.

DIMM numbering

Primary system board (processors 1 and 2) (on page 36)
Secondary system board (processors 3 and 4) (on page 37)
Hardware options installation 35