The terms 32-bit and 64-bit refer to the way a computer’s processor (also called a CPU), handles information.
 

xx-bit format refers to the width of the CPU’s register.
The register is a small amount of storage used by the CPU where the CPU keeps the data it needs to access the quickest in order for optimum computer performance.
The bit designation refers to the width of the register, thus a 64-bit register can hold more data than a 32-bit register.

The 64-bit version of Windows handles large amounts of random access memory (RAM) more effectively than a 32-bit system.

32-bit operating systems are referred to as x86 and 64 bit operating systems as x64.
On a 32-bit operating system, maximum of 4 gigabytes of RAM is allowed.
On a 64-bit operating system, there is no limit.

Most programs designed for the 32-bit version of Windows will work on the 64-bit version of Windows. Notable exceptions are many antivirus programs.

If the program is specifically designed for the 64-bit version of Windows, it won’t work on the 32-bit version of Windows.

All hardware devices need 64-bit drivers to work on a 64-bit version of Windows. Drivers designed for 32-bit versions of Windows won’t work on computers running 64-bit versions of Windows.