Benefits of 64-bit JVM on 64-bit OS and Hardware:

• Wider datapath: The pipe between RAM and CPU is doubled, which improves the performance of memory-bound applications.

• 64-bit memory addressing gives virtually unlimited (1 exabyte) heap allocation. However large heaps affect garbage collection.

• Applications that run with more than 1.5GB of RAM (including free space for garbage collection optimization) should utilize the 64-bit JVM.

• Applications that run on a 32-bit JVM and do not require more than minimal heap sizes will gain nothing from a 64-bit JVM. Barring memory issues, 64-bit hardware with the same relative clock speed and architecture is not likely to run Java applications faster than their 32-bit cousin.

Installing and Configuring 32-bit Sun JDK 5.0 on Linux

• Download the Sun JDK 5.0 (Java 2 Development Kit) from Sun's website: http://java.sun.com/javase/downloads/index_jdk5.jsp. Choose "JDK 5.0 Update <x>" (where x is the latest update number) for download and then select "RPM in self-extracting" file for Linux^[1]. Read the instructions on Sun's website for installing the JDK.

• If you don't want to use SysV service scripts you can install the "self-extracting file" for Linux instead of choosing the "RPM in self-extracting" file. In that case you can skip the next step mentioned here. But it is recommended to use the SysV service scripts for production servers.

• Download and install the appropriate -compat RPM from JPackage here. Please ensure you choose a matching version of the -compat package to the JDK you installed.

• Create an environment variable that points to the JDK installation directory and call it JAVA_HOME. Add $JAVA_HOME/bin to the system path to be able to run java from the command line. You can do this by adding the following lines to the .bashrc file in your home directory.

  #In this example /usr/java/jdk1.5.0_14 is the JDK installation directory.
  export JAVA_HOME=/usr/java/jdk1.5.0_14
  export PATH=$PATH:$JAVA_HOME/bin
  

  Set this variable for the user account doing the installation and also for the user account that will run the server.

• If you have more than one version of JVM installed in your machine, make sure you are using the JDK1.5 installation as the default source for the java and javac executables. You can do this using the alternatives system. The alternatives system allows different versions of Java, from different sources to co-exist on your system.

  Select alternatives for java, javac and java_sdk_1.5.0

  • As root, type the following command at the shell prompt and you should see something like this:

    [root@vsr ~]$ /usr/sbin/alternatives --config java
    There are 2 programs which provide 'java'.
    Selection    Command
    -----------------------------------------------
       1           /usr/lib/jvm/jre-1.4.2-gcj/bin/java
    *+ 2           /usr/lib/jvm/jre-1.5.0-sun/bin/java
    Enter to keep the current selection[+], or type selection number:
    

    Make sure the Sun version [jre-1.5.0-sun in this case] is selected (marked with a '+' in the output), or select it by entering its number as prompted.

  • Repeat the same for javac and java_sdk_1.5.0.

    [root@vsr ~]$ /usr/sbin/alternatives --config javac
    There are 1 programs which provide 'javac'.
    	Selection   Command
    -----------------------------------------------
    *+ 1           /usr/lib/jvm/java-1.5.0-sun/bin/javac
    Enter to keep the current selection[+], or type selection number:
    

    [root@vsr ~]$ /usr/sbin/alternatives --config java_sdk_1.5.0
    There are 1 programs which provide 'java_sdk_1.5.0'.
    	Selection   Command
    -----------------------------------------------
    *+ 1           /usr/lib/jvm/java-1.5.0-sun
    Enter to keep the current selection[+], or type selection number:
    

    You should verify that java, javac and java_sdk_1.5.0 all point to the same manufacturer and version.

  Note

  You can always override this step by setting the JAVA_HOME environment variable as explained in the previous step.

• Make sure that the java executable is in your path and that you are using an appropriate version. To verify your Java environment, type java -version at the shell prompt and you should see something like this:

  [root@vsr ~]$ java -version
  java version "1.5.0_14"
  Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_14-b03)
  Java HotSpot(TM) Client VM (build 1.5.0_14-b03, mixed mode, sharing)
  

Installing and Configuring 32-bit Sun JDK 5.0 on Microsoft Windows

• Download the Sun JDK 5.0 (Java 2 Development Kit) from Sun's website: http://java.sun.com/javase/downloads/index_jdk5.jsp. Choose "JDK 5.0 Update <x>" (where x is the latest update number) for download and then select your Windows Platform options to perform the installation.

• Create an environment variable called JAVA_HOME that points to the JDK installation directory, for example: C:\Program Files\Java\jdk1.5.0_14\. In order to run java from the command line add the jre\bin directory to your path, for example: C:\Program Files\Java\jdk1.5.0_14\jre\bin. To do this, open the Control Panel from the Start Menu, switch to Classic View if necessary, open the System Control Panel applet, select the Advanced Tab, and click on the Environment Variables button.