Dell PowerEdge R620 Technical Manual page 22

Feature
Memory mirroring:
intra-socket
Memory address parity
protection
Memory sparing (rank)
Memory thermal
throttling
For information on memory mirroring and sparing configurations, see the
Owner's Manual
on Dell.com/Support/Manuals.
22 PowerEdge R620 Technical Guide
Description
Memory mirroring is a method of keeping a duplicate (secondary or mirrored)
copy of the contents of memory as a redundant backup for use if the primary
memory fails. The mirrored copy of the memory is stored in memory of the same
processor socket.
This feature provides the ability to detect transient errors on the address lines of
the DDR channel.
Memory sparing allocates one rank per channel as a spare. If excessive correctable
errors occur in a rank or channel, it is moved to the spare area while the operating
system is running to prevent the error from causing an uncorrectable failure.
This feature helps to optimize power/performance and can also be used to
prevent DIMMs from overheating.
Dell PowerEdge R620