IBM NETVISTA 2251 Hardware Maintenance Manual page 41

To install a memory module, do the following:
1. Locate the DIMM connectors.
2. If the retaining clips are not already open, open them.
3. Install the DIMM straight down into the connector until the retaining clips
close. Make sure the notches in the DIMM align with the tabs on the connector.
Notches
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Chapter 5. FRU Replacements