Define the Volatile Keyword Qualifiers in C Language?

The volatile keyword proceed as a data type qualifier and a volatile variable is for dynamic use. E.G. for data that is to be passed to an I/O port. Volatile signify the storage is likely to change at anytime and be changed but something outside the control of the user program. This signify that if you reference the variable the program should always check the physical address (that is a mapped input fifo), and not use it in a cashed way and the volatile statement prevents the compiler optimization.