what is 32 -Bit and 64 -Bit

whats the Difference between 32bit and 64bit

What is a Bit ?

In computing, a bit can be defined as a variable or computed quantity that can have only two possible values. These two values are often interpreted as binary digits and are usually denoted by the numerical digits 0 and 1. The two values can also be interpreted as logical values (true/false, yes/no), algebraic signs (+/−), activation states (on/off), or any other two-valued attribute.  OR  The amount of information that can be stored by a digital device or other physical system that can
usually exist in only two distinct states. These may be the two stable positions of an electrical switch, two distinct voltage or current levels allowed by a circuit, two distinct levels of light intensity, two directions of magnetization or polarization, etc. 

What is the difference between 32-bit and 64-bit versions of Windows? 

The terms 32-bit and 64-bit refer to the way a computer's CPU, handles information. The 64-bit version of Windows handles large amounts of random access memory (RAM) more effectively than a 32-bit system.

What are the Advantages of a 64bit Processor?

1. More greater performance then 32bit Processor.
2. Allowing for the addressing of more of RAM, 64-bit processing can improve video encoding and decoding, CAD, VMs and some other applications.
3. Ability to address memory amounts over four GB, and up to 16 exabytes

What are the Disadvantages of 64bit Processor?

1. You’re currently not able to take full advantage of the technology because the software vendors haven’t made the switch from 32-bit to 64-bit processors.
2. Most AMD Athlon 64 bit processors are expensive, with prices sure to go down in the future.

Note : You can Still use softwares built for 32bit processor but you cannot use 32bit drivers on 64bit processor
Here's a picture of software built for 32bit that works very well on 64bit , its a preview from task manager

32 bit software working in 64bit PC

All the software of 32bits are marked with a asterisk mark and 32 after it as you can see in the preview