IBM System x3850 X5 Implementation Guide

Chapter 3. IBM System x3850 X5 and x3950 X5 85
Figure 3-19 shows eight possible memory configurations for the two memory cards and 16
DIMMs connected to one processor socket. Each configuration has a relative performance
score. Note the key information from this chart:
򐂰 The best performance is achieved by populating all memory DIMMs in two memory cards
for each processor installed (configuration 1).
򐂰 Populating only one memory card per socket can result in approximately a 50%
performance degradation (compare configuration 1 with 5).
򐂰 Memory performance is better if you install DIMMs on all memory channels than if you
leave any memory channels empty (compare configuration 2 with 3).
򐂰 Two DIMMs per channel result in better performance that one DIMM per channel
(compare configuration 1 with 2, and compare configuration 5 with 6).
Figure 3-19 Relative memory performance based on DIMM placement (one processor and two memory cards shown)
Use the following general memory population rules:
򐂰 DIMMs must be installed in matching pairs.
򐂰 Each memory card requires at least two DIMMs.
򐂰 Each processor and memory card must have identical amounts of RAM.
򐂰 Install and populate two memory cards per processor or you can lose memory bandwidth.
1
Each processor:
2 memory controllers
2 DIMMs per channel
8 DIMMs per MC
Mem Ctrl 1 Mem Ctrl 2
1.0
2
Mem Ctrl 1 Mem Ctrl 2
Each processor:
2 memory controllers
1 DIMM per channel
4 DIMMs per MC
0.94
Mem Ctrl 1
Memory card
DIMMs
Channel
Memory buffer
SMI link
Memory controller
3
Mem Ctrl 1 Mem Ctrl 2
Each processor:
2 memory controllers
2 DIMMs per channel
4 DIMMs per MC
0.61
Relative
performance
4
Mem Ctrl 1 Mem Ctrl 2
Each processor:
2 memory controllers
1 DIMM per channel
2 DIMMs per MC
0.58
5
Mem Ctrl 1 Mem Ctrl 2
Each processor:
1 memory controller
2 DIMMs per channel
8 DIMMs per MC
0.51
6
Mem Ctrl 1 Mem Ctrl 2
Each processor:
1 memory controller
1 DIMM per channel
4 DIMMs per MC
0.47
7
Mem Ctrl 1 Mem Ctrl 2
Each processor:
1 memory controller
2 DIMMs per channel
4 DIMMs per MC
0.31
8
Mem Ctrl 1 Mem Ctrl 2
Each processor:
1 memory controller
1 DIMM per channel
2 DIMMs per MC
0.29
1
0.94
0.61
0.51
0.47
0.31
0.29
0.58
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
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Configuration
Relative memory performance
Memory configurations

IBM System x3850 X5 Specifications

General

Brand	IBM
Model	System x3850 X5
Category	Server
Language	English