Dell Precision WorkStation 420 Memory Upgrade Procedure page 8

1-4 System Memory Upgrade

    
      
When you add RIMMs, you must install them in matched pairs (pairs of identical
capacity). If only one pair of RIMMs is installed, they must occupy sockets RIMMB_1
and RIMMA_2, and you must install continuity RIMMs (CRIMMs) in sockets
RIMMB_3 and RIMMA_4.
Table 1-1 lists sample memory configurations.
      
 +)  
  
 1"
128 MB 64 MB
256 MB 64 MB
256 MB 128 MB
512 MB 128 MB
Socket RIMMB_1
Socket RIMMA_2
Socket RIMMB_3
Socket RIMMA_4
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64 MB CRIMM
64 MB 64 MB
128 MB CRIMM
128 MB 128 MB
top of system
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CRIMM
64 MB
CRIMM
128 MB