Monday, August 3, 2009

How to find JVM is 32bit or 64bit ?

You might think it's something simple like typing java -version to find , yes it is for most Java versions, except for Sun JDK 32-bit version doesn't explicitly say which is causing confusion to many users which kind of prompted me to write this article.

If you run java -version in Sun HotSpot 1.6 VM , you will see the below output showing nothing about the bit on the 32-bit JVM where as in 64-bit JVM it explicitly says. so based on this you can almost be kind of sure it's a 32-bit JVM when no bit information shows up in the output.

java version "1.6.0"Java(TM) SE Runtime Environment (build 1.6.0-b105)
Java HotSpot(TM) Client VM (build 1.6.0-b105, mixed mode, sharing)

or
java -version -server from the jdk directory

java version "1.6.0"Java(TM) SE Runtime Environment (build 1.6.0-b105)
Java HotSpot(TM) Server VM (build 1.6.0-b105, mixed mode)

Java(TM) SE Runtime Environment (build 1.6.0_11-b03)
Java HotSpot(TM) 64-Bit Server VM (build 11.0-b16, mixed mode)

Whereas on the other hand IBM JDK versions seems to explicitly say what type of JVM it is for both 32-bit as well as 64-bit.

Java(TM) SE Runtime Environment (build pwi3260sr2-20080818_01(SR2))
IBM J9 VM (build 2.4, J2RE 1.6.0 IBM J9 2.4 Windows XP x86-32 jvmwi3260-20080816_22093 (JIT enabled, AOT enabled)

Also when you try to run with 64-bit model on the 32-bit JVM it might complain as below,

java -d64 -server -version
Running a 64-bit JVM is not supported on this platform.

Also you can look at the lib directory of the jre and see if there is any subdirectory ends with 64 like /opt/jdk1.6.0_11/jre/lib/amd64/ confirming that it's a 64-bit jvm. On a running jvm run Linux command: lsof -p pid of java and see where the libjvm.so process are loaded, which might indicate the type of JVM.

Note there is no such thing as WebSphere Application Server 64-bit or 32-bit version , basically it depends on what kinf of JVM (32-bit 0r 64-bit) you are running on.

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