System Call vs Procedure Call: Understanding the Differences

In computer science, two commonly used terms are system call and procedure call. Although both are used to transfer control from one part of a program to another, there are important differences between the two. In this article, we will explore the differences between system calls and procedure calls.

What is a System Call?

A system call is a way for a program to request a service from the operating system (OS). The program makes a system call by issuing a special instruction that interrupts the normal flow of the program and transfers control to the kernel, which is the core component of the OS.

System calls are used for a wide range of purposes, including accessing hardware devices, managing memory, and performing file operations. Some examples of system calls in popular operating systems include read and write operations on files, opening and closing network connections, and allocating memory.

What is a Procedure Call?

A procedure call is a way for a program to invoke a subroutine or a function that is part of the same program. When a procedure call is made, control is transferred to the subroutine, and the subroutine executes a set of instructions before returning control back to the calling program.

Procedure calls are commonly used in programming languages to break down a large program into smaller, more manageable pieces. By separating a program into smaller procedures, the code becomes easier to read, understand, and maintain.

Differences between System Calls and Procedure Calls

Purpose

The main difference between system calls and procedure calls is their purpose. System calls are used to request services from the operating system, whereas procedure calls are used to invoke subroutines or functions that are part of the same program.

Performance

System calls are generally slower than procedure calls, due to the overhead involved in switching between user mode and kernel mode. When a program makes a system call, control is transferred to the kernel, which involves a context switch and a change in memory protection modes. This overhead can have a significant impact on the performance of a program that makes frequent system calls.

On the other hand, procedure calls are faster than system calls, since they don’t involve a context switch or a change in memory protection modes. Procedure calls simply involve transferring control to another part of the same program, which can be done quickly and efficiently.

Security

System calls are subject to security checks and restrictions, since they involve accessing privileged resources such as hardware devices and system files. In order to make a system call, a program must have the necessary permissions and privileges.

Procedure calls, on the other hand, are not subject to security checks, since they are part of the same program and operate within the same security context.

Best Use Cases for System Calls and Procedure Calls

In general, you should choose system calls or procedure calls based on the specific needs of your program. Here are some guidelines to help you decide:

• Use system calls when you need to access privileged resources or services provided by the operating system.
• Use procedure calls when you need to break down a large program into smaller, more manageable pieces.

Conclusion

In summary, system calls and procedure calls are both important mechanisms for transferring control between different parts of a program. While system calls are used to request services from the operating system, procedure calls are used to invoke subroutines or functions that are part of the same program. By understanding the differences between system calls and procedure calls, you can choose the best mechanism for your specific programming needs.

FAQs

1. Can a program make a system call and a procedure call at the same time?
   • Yes, a program can make both system calls and procedure calls, depending on its specific needs.
2. Can system calls be made from within a procedure call?
   • Yes, a program can make a system call from within a procedure call, although this may not be the most efficient approach depending on the specific use case.
3. Can procedure calls be made between different programs?
   • No, procedure calls are limited to invoking subroutines or functions within the same program.
4. Can system calls be made between different programs?
   • Yes, system calls can be made between different programs, but this is typically done through inter-process communication mechanisms such as pipes, sockets, or shared memory.
5. How can I determine which mechanism to use in my programming project?
   • The decision to use system calls or procedure calls will depend on the specific needs of your program. If you need to access privileged resources or services provided by the operating system, you should use system calls. If you need to break down a large program into smaller, more manageable pieces, you should use procedure calls.