Java's "os.arch" System Property is the Bitness of the JRE, NOT the Operating System

5946627a02755f64961995d902eafa07e58a323c

Mon 19 Oct 2009 11:15:00 -0800

If you ever use Java to check if a system is 32 or 64-bit, you should know that Java’s os.arch system property returns the bitness of the JRE, not the OS itself. Sites like this are WRONG — any resource that claims Java’s os.arch property returns the real “architecture of the OS” is lying. Case in point, I recently ran this tiny program on a 64-bit Windows 7 machine, with a 32-bit JRE:

import com.sun.servicetag.SystemEnvironment;

public class OSArchLies {

  public static void main(String[] args) {

    // Will say "x86" even on a 64-bit machine
    // using a 32-bit Java runtime
    SystemEnvironment env =
        SystemEnvironment.getSystemEnvironment();
    final String envArch = env.getOsArchitecture();

    // The os.arch property will also say "x86" on a
    // 64-bit machine using a 32-bit runtime
    final String propArch = System.getProperty("os.arch");

    System.out.println( "getOsArchitecture() says => " + envArch );
    System.out.println( "getProperty() says => " + propArch );

  }

}

The output from this tiny app on a 64-bit box:

#/> java OSArchLies
getOsArchitecture() says => x86
getProperty() says => x86

In this case, one would expect to see something like x86_64 or amd64 instead of just x86. Bottom line, don’t believe what you read about os.arch and other Java system properties. They are usually properties of the JRE/JDK itself, and not necessarily the real properties of the underlying OS or architecture. If you need to check if a system is actually 32 or 64-bit, you should look elsewhere in the system registry or write your own native app and call it from Java.