To identify the appropriate key, first determine the ORACLE_HOME directory that your Oracle Instance is running from. You can do this as follows:
1. Go to the services console by running services.msc
2. Identify the service for your instance. In this example, we will use an instance name of TEST1, so we have a service called 'OracleServiceTEST1'
3. Right-Click on the OracleServiceTEST1 service and choose 'Properties'. On the 'General' tab there will be a line titled 'Path to Executable'. This will be the path to the BIN directory of your ORACLE_HOME
4. Next, using Windows Explorer, go to that ORACLE_HOME\bin directory and find a file called 'oracle.key'. Open this file using a text editor such as Wordpad or Notepad.
5. This file will give you the registry key information for the key associated with that particular home. The contents of the file will look something like this: SOFTWARE\ORACLE\KEY_OraDb10g_home1
This key is actually under HKEY_LOCAL_MACHINE, so the full key path would be:
6. Open the registry via regedit and navigate to the key identified in Step#5 above. With the key for the database home highlighted, go to the Regedit Menu and choose Edit->New->String Value
7. Give the key a name of ORA_TEST1_LPENABLE (In our example, we are using a SIDNAME of TEST1, but you will substitute your sidname as appropriate.
8. After creating the new value, double-click on it and set it to a value of 1 to enable Large Page Support for that instance.
9. You will need to stop the OracleServiceTEST1 service, and restart it, in order for the change to take affect. If the instance is running, it should be shutdown cleanly (via SQLPLUS, for example) before the service is stopped.
10. Note that if this is a RAC system, and you want instances on all nodes to use Large Pages, then you will have to add the value to the registry key on all nodes. You can stop/restart the OracleServices in a rolling fashion, in order to avoid a full outage.