HP 421 Notebook-PC - Manual (Page 101)

9 Memory modules
The computer has one memory module compartment, which is located on the bottom of the
computer.
The memory capacity of the computer can be upgraded by adding a memory module to the vacant
expansion memory module slot or by upgrading the existing memory module in the primary memory
module slot.
All memory modules installed in the computer must be the same type. When upgrading memory
capacity, verify that the upgrade modules are the same type as those already installed in the
computer.
WARNING! To reduce the risk of electric shock and damage to the equipment, unplug the power
cord and remove all batteries before installing a memory module.
CAUTION: Electrostatic discharge (ESD) can damage electronic components. Before beginning
any procedure, touch a grounded metal object to be sure that you are discharged of static electricity.
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