NEC Express5800 Series User Manual page 71

Chapter 2 Preparations
Memory Lock Step cannot be configured in the following cases:

Memory Lock Step between memory channels of different memory controllers (CPU)

Memory Lock Step within the same memory channel
Notes on Configuring Lock Step
If you additionally install or remove DIMMs that unable to configure Memory LockStep configuration, Memory
RAS Mode is changed to "Independent".
"LockStep" is removed from Advanced  Memory Configuration  Memory Information  CPUx_DIMMx
Status xxxx MB (LockStep) in BIOS SETUP.
Express5800/T120g User's Guide
1. Installing Internal Optional Devices
71