32 bit OS or 64 bit OS?

Source

Follow the steps to determine the bit count of your operating system.
Windows Vista
Method 1: View System window in Control Panel
1. Click Start, type system in the Start Search box
and then click System in the Programs list.
2. The operating system is displayed 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: View System Information window
1. Click Start, type system in the Start Search box, and then click System Information in the Programs list.
2. When System Summary is selected in the navigation pane, the operating system is displayed 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.

Windows XP
Method 1: View System Properties in Control Panel
1. Click Start, and then click Run.
2. Type sysdm.cpl, and then click OK.
3. Click the General tab. The operating system is displayed as follows:

• For a 64-bit version operating system:
  Windows XP Professional x64 Edition Version < Year> appears under System.
• For a 32-bit version operating system:
  Windows XP Professional Version < Year> appears under System.

Note <Year> is a placeholder for year.
Method 2: View System Information window
1. Click Start, and then click Run.
2. Type winmsd.exe, and then click OK.
3. When System Summary is selected in the navigation pane, the operating system is displayed 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.