JAVA SIM CARDS come in two basic types of smart CARDS.Storage smart CARDS are common erasable storage devices;It is typically characterized by literacy and possibly security features.A more sophisticated version -- the processor smart card -- is a very small, portable computing device that can fit in your wallet.Java-based smart CARDS fall into the latter category.They store data in an integrated microprocessor chip.The applet is then downloaded into the memory of the microprocessor and run by the Java virtual machine.Similar to MULTOS, another smart card development technology, the Java card enables multiple applications to be installed and coexist independently.Each applet is protected by a firewall to maintain its integrity and prevent interference.Applications can be dynamically upgraded.