Dell PowerEdge 2970 Handbuch Seite 12

The 8-GB DIMMs that are supported on your system are quad-rank modules.
Using quad-rank DIMMs in a memory sparing configuration provides a
proportionally smaller amount of spared memory than using single- or dual-
rank DIMMs in a similar configuration. Because memory sparing allocates
spared memory by DIMM ranks, one-fourth of a quad-rank DIMM (one rank
out of four) is spared instead of one-half of a dual-rank DIMM or the full
capacity of a single-rank DIMM. Table 1-4 supersedes the information
provided in your Hardware Owner's Manual regarding memory sparing
configurations that are supported on your system.
Table 1-4. Memory Sparing in Single- and Dual-Processor Configurations
Processor 1
DIMM
Pair 1/2 Pair 3/4
512 MB 512 MB
1 GB 512 MB
1 GB 1 GB
2 GB 512 MB
2 GB 1 GB
2 GB 2 GB
4 GB 512 MB
4 GB 1 GB
4 GB 2 GB
4 GB 4 GB
8 GB 8 GB
Indicates a spared single-rank DIMM (512-MB or 1-GB). The entire capacity
of this DIMM is reserved for sparing.
Indicates a spared dual-rank DIMM (2-GB or 4-GB). One-half of this DIMM's
capacity is reserved for sparing.
8-GB DIMMs are quad-rank. One-fourth of this DIMM's capacity is reserved
for sparing.
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Information Update
Processor 2
DIMM DIMM
Pair 5/6
512 MB
1 GB
1 GB
2 GB
2 GB
2 GB
4 GB
4 GB
4 GB
4 GB
8 GB
Available
Memory
DIMM
Pair 7/8 1 CPU / 2 CPUs 1 CPU / 2 CPUs
512 MB 1 GB / 2 GB
512 MB 1 GB / 2 GB
1 GB 2 GB / 4 GB
512 MB 3 GB / 6 GB
1 GB 4 GB / 8 GB
2 GB 6 GB / 12 GB
512 MB 5 GB / 10 GB
1 GB 6 GB / 12 GB
2 GB 8 GB / 16 GB
4 GB 12 GB / 24 GB 4 GB / 8 GB
8 GB 28 GB / 56GB 4 GB / 8 GB
Spared
Memory
1 GB / 2 GB
2 GB / 4 GB
2 GB / 4 GB
2 GB / 4 GB
2 GB / 4 GB
2 GB / 4 GB
4 GB / 8 GB
4 GB / 8 GB
4 GB / 8 GB