Interrupt vs. System Calls

Attribute	Interrupt	System Calls
Definition	Signal to the processor to suspend its current operation and handle a specific event	Request to the operating system to perform a specific task on behalf of the user program
Trigger	Hardware or software event that requires immediate attention	User program explicitly makes a request to the operating system
Handling	Handled by the processor's interrupt handler routine	Handled by the operating system's system call handler routine
Privilege Level	Can be triggered at any privilege level	Usually requires a switch to a higher privilege level to execute
Overhead	Generally faster and has lower overhead	Slower and has higher overhead due to context switching

Introduction

Interrupts and system calls are two fundamental concepts in computer science that play a crucial role in the functioning of operating systems. While both are mechanisms used to handle events that require the attention of the operating system, they differ in their implementation and purpose. In this article, we will explore the attributes of interrupts and system calls, highlighting their differences and similarities.

Interrupts

Interrupts are signals sent by hardware devices to the CPU to request immediate attention. They can occur at any time during the execution of a program and are used to handle events such as I/O operations, hardware errors, and timer expirations. When an interrupt occurs, the CPU suspends the current program execution and transfers control to a specific interrupt handler, which is a piece of code responsible for handling the interrupt.

There are several types of interrupts, including hardware interrupts, software interrupts, and exceptions. Hardware interrupts are generated by external devices, such as keyboards or disk drives, while software interrupts are triggered by software instructions. Exceptions, on the other hand, are unexpected events that disrupt the normal flow of execution, such as division by zero or invalid memory access.

Interrupts are asynchronous events, meaning they can occur at any time without the explicit request of the program. This makes them essential for handling real-time events and ensuring the responsiveness of the system. However, interrupts can also introduce complexity and overhead, as the CPU must switch between different tasks rapidly to handle multiple interrupts simultaneously.

System Calls

System calls, on the other hand, are a mechanism used by user programs to request services from the operating system. They provide a way for user programs to interact with the underlying hardware and perform privileged operations, such as reading from a file or creating a new process. System calls are typically implemented as software interrupts, where the user program triggers an interrupt to transfer control to the operating system.

System calls are synchronous events, meaning they are initiated by the user program and require explicit invocation. When a system call is made, the CPU switches from user mode to kernel mode, granting the operating system access to privileged resources. The operating system then executes the requested operation on behalf of the user program and returns the result back to the user.

System calls provide a secure and controlled way for user programs to interact with the operating system, ensuring that only authorized operations are performed. They also help in maintaining the stability and security of the system by enforcing access control policies and preventing unauthorized access to system resources.

Comparison

While interrupts and system calls serve different purposes and operate in distinct ways, they share some common attributes. Both interrupts and system calls involve a context switch, where the CPU transitions from user mode to kernel mode to handle the event. This transition involves saving the state of the current program and restoring it after the event has been processed.

Another similarity between interrupts and system calls is that they both require the involvement of the operating system. In the case of interrupts, the operating system provides interrupt handlers to respond to hardware events, while in the case of system calls, the operating system implements system call handlers to execute user requests.

Conclusion

In conclusion, interrupts and system calls are essential mechanisms in operating systems that enable communication between user programs and the underlying hardware. While interrupts are used to handle asynchronous events generated by hardware devices, system calls provide a way for user programs to request services from the operating system. By understanding the attributes of interrupts and system calls, developers can design efficient and reliable systems that meet the needs of users and applications.