Definition: In the personal computing world, 32-bit and 64-bit refer to the type of central processing unit, operating system, driver, software program, etc. that utilizes that particular architecture.
32-bit hardware and software is often referred to as x86 or x86-32. 64-bit hardware and software is often referred to as x64 or x86-64.
32-bit systems utilize data in 32-bit pieces while 64-bit systems utilize data in 64-bit pieces. In general, the more data that can be processed at once, the faster the system can operate. There are several other advantages to a 64-bit system as well, most practically the ability to use significantly greater amounts of physical memory.
Most new processors today are based on the 64-bit architecture and support 64-bit operating systems. These processors are also fully compatible with 32-bit operating systems.
Most editions of Windows 7 and Windows Vista are available in 64-bit format. Only Windows XP Professional is available in 64-bit. All editions of Windows 7, Windows Vista, and Windows XP are also available in 32-bit.