Lenovo System x3850 X6 and x3950 X6 Quick Start Guide
5
Memory subsystem
The memory subsystem can operate in one of the following modes:
Independent (Performance) mode
Lockstep (RAS) mode
In
Performance
mode, each channel on an SMI is addressed independently, essentially
providing the ability to run two transactions at once. In
Lockstep
mode, a pair of DIMMs
spread across both channels on an SMI is addressed simultaneously. Lockstep mode
provides higher memory frequency and memory reliability (Double Device Data Correction
+1 bit) but at the expense of higher memory bandwidth. Conversely, Independent mode
provides higher memory bandwidth at the cost of advanced memory RAS features and
memory frequency (Single Device Data Correction only).
Figure 4 shows the two memory modes.
Figure 4 Memory modes: Performance mode (left) and RAS mode (right)
Intel Xeon processor
DIMM
Memory
controller
DIMM
DIMM
Memory
controller
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
Memory
buffer
Memory
buffer
Memory
buffer
Memory
buffer
Data 1
Data 0
Intel Xeon processor
DIMM
Memory
controller
DIMM
DIMM
Memory
controller
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
DIMM
Memory
buffer
Memory
buffer
Memory
buffer
Memory
buffer
Data
Lockstep
channel
SMI2
links
DDR3
links
Memory performance mode
Memory RAS mode
