Dell Precision T7400 (Late 2007) - Manual (Page 173)

Adding and Replacing Parts 173
NOTICE: Full-length heat spreaders (FLHS) are required for all DIMMs.
NOTE: Memory purchased from Dell is covered under your computer warranty.
Fully Buffered DIMM (FBD) Memory Overview
For optimal performance, fully buffered DIMMs (FBDs) should be installed
in matched sets of four. This enables quad-channel operation and provides
the highest memory bandwidth. The sets of four must be matched in size,
rank, and organization. This information can normally be found on the FBD
label. For example, the label of each FBD in a set of four might read: 1G 2R
x8, in which 1G represents the size of the memory module, 2R represents the
number of ranks, and x8 represents the organization.
NOTICE: Full-length heat spreaders (FLHS) are required for all memory.
Memory Installation
Fully buffered DDR2 memory modules can also be installed in pairs of two; in
this case, the computer will continue to operate, but with a slight reduction
in performance. The pairs must be matched in size, rank, and organization.
Install memory modules in order of their labels on the system board; matched
sets of four should be installed first into DIMM slots 1-4 and then into
DIMM slots 5-8 on the system board. Pairs of memory should be first
installed into slots DIMM_1, and DIMM_2, then DIMM_3 and DIMM_4,
and so on.
1 fully buffered DIMM 2 information label
1
2