Difference between Trap and Interrupt in Operating System

In this article, you will learn about the difference between the trap and interrupt. But before discussing the differences, you must need to know about the trap and interrupt.

What is the trap?

Traps are occurred by the user program to invoke the functionality of the OS. Assume the user application requires something to be printed on the screen, and it would set off a trap, and the operating system would write the data to the screen.

A trap is a software-produced interrupt that can be caused by various factors, including an error in instruction, such as division by zero or illegal memory access. A trap may also be generated when a user program makes a definite service request from the OS.

Traps are called synchronous events because the execution of the present instructions much more likely causes traps. System calls are another type of trap in which the program asks the operating system to seek a certain service, and the operating system subsequently generates an interrupt to allow the program to access the services.

The traps are more active as an interrupt because the code will heavily depend on the fact that the trap may be used to interact with the OS. Therefore, traps would repeat the trap's function to access any system service.

Mechanism of Trap in the Operating System

The user program on the CPU usually makes use of library calls to make system calls. The library routine check's job is to validate the program's parameters, create a data structure to transfer the arguments from the application to the operating system's kernel, and then execute special instructions known as traps or software interrupts.

These special instructions or traps has operands that aid in determining which kernel service the application inputs require. As a result, when the process is set to execute the traps, the interrupt saves the user code's state, switches to supervisor mode, and then dispatches the relevant kernel procedure that may offer the requested service.

What is the Interrupt?

Interrupts are signals emitted by software or hardware when a process or event requires immediate attention. Because both hardware and software generate these signals, they are referred to as the hardware, and the software interrupts. A hardware device produces an interrupt. Interrupts can be caused by a USB device, a NIC card, or a keyboard. Interrupts happen asynchronously, and they may happen at any time.

An interrupt pin is a dedicated pin on a CPU. It is also known as the INT pin. The interrupt pin connects devices like keyboards to the processor. When a key is clicked, the interrupt occurs. The CPU will transition from the current process to an Interrupt Handler Routine. In this case, the keyboard interrupt handler routine is occurring. After finishing the interrupt handler code, the CPU returns to the original program that was running. When an interrupt arrived, the CPU changes the context and executes the interrupt handler. It returns to the previous state after completion.

A CPU has a single interrupt pin, but there are several hardware devices. The interrupt controller allows several pins to share a single interrupt pin. To identify which device caused the interrupt, the processor would interact with the interrupt controller, executing the appropriate interrupt handler procedure. It could be a method for handling timer, USB, or keyboard interrupts.

Mechanism of Interrupt in Operating System

Let's look at how the interrupt works. Multiple instructions are executed in a program, and the time it takes one program to execute one instruction of the program is referred to as the instruction cycle. I/O devices or user programs may generate interruptions while the CPU is executing the program's instructions. These interruptions would be passed to it as input while the CPU is executing the program's instructions.

The processor manages interrupts by checking whether or not an interrupt is pending to take action after each instruction cycle. If the CPU does not identify any pending interrupts, it will proceed to the next program instruction. If the CPU identifies a pending interrupt, it will stop the execution of the instruction and invoke the interrupt handler program to serve the pending interrupt.

Main differences between the trap and interrupt

Here, you will learn the main differences between the trap and interrupt in the operating system. There are differences between the trap and interrupt in the operating system. Some of the differences are as follows:

1. The trap is a signal raised by a user program instructing the operating system to perform some functionality immediately. In contrast, the interrupt is a signal to the CPU emitted by hardware that indicates an event that requires immediate attention.
2. A trap also triggers OS functionality. It gives control to the trap handler. In contrast, an interrupt triggers the CPU to perform the interrupt handler routine.
3. A trap is synchronous and may occur after the execution of the instruction. In contrast, an interrupt is asynchronous and may occur at any time.
4. A trap is generated by a user program instruction. In contrast, the hardware devices generate an interrupt.
5. A trap is also known as a software interrupt. In contrast, an interrupt is known as a hardware interrupt.
6. The trap is a synchronous process. In contrast, the interrupt is an asynchronous process.

Head-to-head comparison between the trap and interrupt

Here, you will learn the head-to-head comparison between the trap and interrupt in the operating system. There are differences between the trap and interrupt in the operating system. Some of the differences are as follows:

Conclusion

There are two kinds of events: traps and interrupts. The difference between a trap and an interrupt is that a trap is triggered by a user program to invoke OS functionality. Still, an interrupt is triggered by a hardware device to allow the processor to execute the corresponding interrupt handler routine.