I'm using JPCSP 64bit with Windows 7 Ultimate 64 and I've noticed that it's using only 2GB of RAM and my machine has 4GB available. Would it be possible to make JPCSP faster by making it to use 4GB instead of 2GB? How can I increase memory usage in JPCSP?
You could increase the Java Heap by replacing "-Xmx1024m" for something higher but remember that RAM memory will not give you an important speed boost since RAM is just the process information that have to be process on the CPU; think on it like a waiting room where process are waiting for being processed and 2GB can be enough to the game you are playing.
The easier and faster way to speed up JPCSP is upgrading your PC hardware; however, if it is not an option for you, try some work around on JPCSP options like decreasing the MaximumCompilerMethod, Enable Vertex Cache or run it with JPCSP launcher who provides important Java commands that may help you.