Fujitsu PRIMERGY RX4770 M5 - Rank Sparing Mode

Mirrored Channel mode - 4 CPUs populated
.
10.2.3.3 Rank Sparing mode
Single-rank/dual-rank RDIMM modules - 2 CPUs populated (if all modules
have the same capacity)
.
Main memory
RX4770 M5 Upgrade and Maintenance Manual 249