Operation System: 32-bit or 64-bit (x86 or x64)?

Source
If you want to find out whether the system is installed with a 32-bit or 64-bit (Microsoft labels them as x86 or x64) based operating system, which requires specifically built software application (See x86 or x64 OS)
Windows Vista

Method 1

1. Click Start, then click on Run or Start Search.
2. Type msinfo32.exe and then press Enter key.
3. In “System Information”, review the value for the System Type item:
   • For 32-bit editions of Windows, the value of the System Type item is x86-based PC.
   • For 64-bit editions of Windows, the value of the System Type item is x64-based PC.

Method 2

1. Click Start, type system in the “Start Search” box, and then click system in the “Programs” list.
2. The operating system appears as follows:
   • For a 64-bit version operating system: 64-bit Operating System appears for the “System type” under “System”.
   • For a 32-bit version operating system: 32-bit Operating System appears for the “System type” under “System”.

Method 3

1. Click Start, type system in the “Start Search” box, and then click System Information in the “Programs” list.
2. The operating system appears as follows:
   • For a 64-bit version operating system: x64-based PC appears for the “System type” under “Item”.
   • For a 32-bit version operating system: x86-based PC appears for the “System type” under “Item”.

Microsoft Windows XP Professional

Method 1

1. Click Start, then click on Run or Start Search.
2. Type msinfo32.exe and then press Enter key.
3. In “System Information”, review the value for the System Type item:
   • For 32-bit editions of Windows, the value of the System Type item is x86-based PC.
   • For 64-bit editions of Windows, the value of the System Type item is x64-based PC.

Method 2

1. Click Start, click Run, type sysdm.cpl, and then click OK.
2. Click the General tab. The operating system appears as follows:
   • For a 64-bit version operating system: Microsoft Windows XP Professional x64 Edition Version appears under System.
   • For a 32-bit version operating system: Microsoft Windows XP Professional Version appears under System.

   Note is a placeholder for a year.

Method 3

1. Click Start, click Run, type winmsd.exe, and then click OK.
2. In the details pane, locate Processor under Item. Note the value.
   • If the value that corresponds to Processor starts with x86, the computer is running a 32-bit version of the Windows operating system.
   • If the value that corresponds to Processor starts with ia64 or AMD64, the computer is running a 64-bit version of the Windows operating system.

Microsoft Windows Server 2003

Method 1

1. Click Start, click Run, type sysdm.cpl, and then click OK.
2. Click the General tab. The operating system appears as follows:
   • For a 64-bit version operating system: Microsoft Windows Server 2003 Enterprise x64 Edition appears under System.
   • For a 32-bit version operating system: Microsoft Windows Server 2003 Enterprise Edition appears under System.

Method 2

1. Click Start, click Run, type winmsd.exe, and then click OK.
2. In the details pane, locate Processor under Item. Note the value.
   • If the value that corresponds to Processor starts with x86, the computer is running a 32-bit version of the Windows operating system.
   • If the value that corresponds to Processor starts with EM64T or ia64, the computer is running a 64-bit version of the Windows operating system.