How to find the OS bit type

I want to know the OS type, means is it of 64bit os or 32bit os. But I am getting different response from 32bit/64bit executable which getting system properties about OS

I am getting details from system property. and I have 64bit machine and OS windows 8.1 X64

        "OS Architecture : " + System.getProperty("os.arch"));

        "OS Name : " + System.getProperty("os.name"));

        "OS Version : " + System.getProperty("os.version")

        "Data Model : " + System.getProperty("sun.arch.data.model"));

While running 64bit Executable getting following response.

OS Architecture : amd64

OS Name : Windows 8

OS Version : 6.2 amd64

Data Model : 64

While running 32bit Executable getting following response.

OS Architecture : x86

OS Name : Windows 8

OS Version : 6.2 x86

Data Model : 32

How can I get OS actual bit type ?