64-bit or 32-bit / x64 or x84

It's always come to the point that we need to know our system is 64-bit or 32-bit / x64 or x84 when we download some installer or choose installation option.

Below is how we determine 64-bit or 32-bit / x64 or x84 for different windows OS.

Windows Vista

Method 1
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 2
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, 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 <year> appears under System.
• For a 32-bit version operating system: Microsoft Windows XP Professional Version <year> appears under System. Note is a placeholder for a year.

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 ia64 or AMD64, the computer is running a 64-bit version of the Windows operating system.

Microsoft Windows Server 2003

Method 1
Click Start, click Run, type sysdm.cpl, and then click OK.
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.

reference: http://support.microsoft.com/kb/827218