Fujitsu D3081 Technical Manual page 26

Features
Table 4 shows the supported DIMM configurations with mixed DIMM RANK.
DIMM# x/2 DIMM# x/1
4 Rank 4 Rank
2 Rank 4 Rank
1 Rank 4 Rank
not installed 4 Rank
2 Rank 2 Rank
1 Rank 2 Rank
not installed 2 Rank
2 Rank 1 Rank
1 Rank 1 Rank
not installed 1 Rank
not installed not installed
Table 4: Supported DIMM configurations with mixed DIMM RANK
26 Technical Manual
D3081, D3131, D3082 (RX900 S1)