If you've recently upgraded the RAM, or are moving your Tomcat applications to a larger box, you may want to update your allocated memory.
To find out how much RAM is allocated already to your Tomcat instance, if you have Tomcat installed as a Windows service, you can run Regedit and look at:
HKEY_LOCAL_MACHINE SOFTWARE Apache Software Foundation Procrun 2,0
Under that key will be all the tomcat service instances you have installed on that machine. If you expand an instance tree you will see another key named Parameters. Expand this and you will see a number of named values: