The Most comman difference are given below

• System calls are heavy. While a procedure call can generally be performed in a few system instructions, a system call needs the computer to save its state, let the operating system take use of the CPU, have the operating system done some function, have the operating system load its state, and then have the operating system send control of the CPU back to user.

• System calls are machine dependent. It could not be a great idea to directly access system calls when portability cannot be used. System calls are also quite hard. Most usually, it adds the duo of RET and TRAP. To develop system call, one would require specialized knowledge of I/O registers, the sequence of operations required to use them; and most important of all, operated enough protection because I/O sources are usually distributed among multiple processes and/or users.