A Java class is a .class file that contains the compiled result of java source files. When a JVM runs a program it dynamically loads the java classes required. When the jserver.class is required it must be loaded from your local file system. Different JVMs have different search paths for class files, but they all search the classpath path. Rather than add the jserver class file to different locations, the J installation updates the classpath environment variable to include the J system\extras\java\classes directory.