HP Compaq dc7100 DT Reference Manual page 201

Removal and Replacement Procedures - Ultra-Slim Desktop (USDT) Chassis
A memory module can be installed in only one way. Match the notch on the module with the tab
on the memory socket.
7. Repeat step 6 for any additional modules that you want to install.
The computer automatically recognizes the additional memory when the computer is turned on.
To reassemble the computer, reverse the removal procedure.
Service Reference Guide, dc7100 361288-003 8–13