As we know that for performing any Operation as user must have to specify the Operation which he wants to Operate on the Computer. We can say that For Performing any Operation a user must have to Request for a Service from the System. For Making any Request a user will prepare a Special call which is also known as the System Call.
The System Call is the Request for Running any Program and for Performing any Operation on the System. When a user First Time Starts the System then the System is in the user Mode and When he request For a Service then the User Mode will be Converted into the Kernel Mode Which just Listen the Request of the user and Process the Request and Display the Results those are Produced after the Processing. When a user Request for Opening any Folder or When a Moves his Mouse his Mouse on the Screen, then this is called as the System call which he is using for performing any Operation.