Table of contents

Introduction

What is a Trap?

2.1.

How Do Traps Work?

What is an Interrupt?

3.1.

How Do Interrupts Work?

Difference between Trap and Interrupt in Operating Systems

Frequently Asked Questions

5.1.

What is an operating system?

5.2.

What do you mean by dual-mode operation in OS?

5.3.

What is a Thread?

5.4.

What is polling?

Conclusion

Last Updated: Mar 27, 2024

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Difference between Trap and Interrupt in Operating System

Q: What is a Thread?

A thread is a single sequence stream within a process. Since threads have some of the properties of processes hence they are sometimes called lightweight processes. Threads are a popular way to improve the application through parallelism.

Author Abhiyodaya Pandey

Introduction

Interrupts and traps are two kinds of events in the Operating System. A trap is triggered by a user application, whereas an interrupt is triggered by a hardware device such as a keyboard, timer, or other device. The control is passed to the trap handler by a trap, and the control is passed to an interrupt handler by an interrupt. Following the execution of the handler, the control returns to the original program.

Difference between Trap and Interrupt in Operating System

In this article, we'll look at two kinds of OS events: traps and interrupts. You will get to know the difference between Trap and Interrupt in Operating System, along with their working.

What is a Trap?

A trap is a synchronous interrupt that is triggered by an exception in a user process to allow functionality to be executed. A trap in an operating system can be triggered by exception situations such as improper memory access, division by zero, or a breakpoint.

A trap switches an operating system into kernel mode. The OS then performs some actions before returning control to the previous process. During a trap, the execution of a process takes precedence over user code. When the operating system detects a trap, it halts the user process. The OS resumes and continues the execution of the user processes as soon as the system call is completed.

As an example, consider the following. Assume you have a statement like printf ("%s\n", str); This will call the write function to print the output to the standard output, which is the monitor. This will set off a trap and send control to the trap handler. The user mode then switches to kernel mode, and the OS executes the write call. After the task is completed, the control is returned to user mode from kernel mode.

How Do Traps Work?

The stages listed below can be used to summarize how a trap works in an operating system:

Errors or exceptions that may occur while a program is being performed include a divide-by-zero error, an attempt to access erroneous memory and an invalid instruction. After identifying the error or exception the CPU generates a trap signal
The CPU enters kernel mode with the help of this signal and transfers control to the trap handler which is a predefined region of the operating system
The trap handler in the operating system determines the source of the trap and performs the appropriate action. This could include terminating the application telling the user of an error or providing a specific function requested by the program
After the trap handler has completed its task control is restored to the program that created the trap and the CPU returns to user mode

What is an Interrupt?

An interrupt is raised by a hardware device. USB devices, NIC cards, and keyboards can cause interrupts. Interrupts are asynchronous. Therefore, they can occur at any time.

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

Although a processor only has one interrupt pin, there are numerous hardware devices. The interrupt controller facilitates the sharing of a single interrupt pin among many pins. To discover which device caused the interrupt, the processor will connect with the interrupt controller. The CPU will then execute the associated interrupt handler routine.

How Do Interrupts Work?

The stages listed below summarize how an interrupt works in an operating system:

An interrupt signal is generated by an external hardware device to notify the CPU that something has to be done. Because the CPU suspends the execution of the currently running program and enters kernel mode, the operating system may handle the interrupt
The operating system invokes its interrupt handler to handle the interrupt. When an interrupt occurs, the interrupt handler determines its cause and responds properly by reading data from the device or doing other input/output (I/O) operations
After the interrupt has been handled, the interrupted program resumes execution at the point where it was suspended

Difference between Trap and Interrupt in Operating Systems

S.No	Traps	Interrupt
1	The trap is a signal sent by user software to the operating system instructing it to perform a specific action immediately.	The interrupt is a hardware signal that informs the CPU that something urgent has to be addressed right away.
2	It is a synchronized process.	It is an asynchronous process.
3	It is generated by a user program instruction.	They are produced by hardware.
4	Another term for it is software interrupt.	It is also known as a hardware interrupt.
5	All traps are interrupt.	Not all the interrupts are traps.
6	The operating system's specialized functionality is carried out, and control is passed to the trap handler.	It forces the Processor to run a specific interrupt handler software.

Frequently Asked Questions

What is an operating system?

An operating system is a program that is loaded into the memory of a computer after it boots up. It is the application that serves as a communication layer between the user or applications and the hardware of the system. It handles a variety of activities such as work scheduling, memory, storage, and resource management.

What do you mean by dual-mode operation in OS?

Dual-mode operation in an OS (operating system) refers to the system's capacity to move between two modes of operation for compute processes while avoiding system crashes. There are two kinds of operations: user and kernel.

What is a Thread?

A thread is a single sequence stream within a process. Since threads have some of the properties of processes hence they are sometimes called lightweight processes. Threads are a popular way to improve the application through parallelism.

What is polling?

Polling refers to the earlier method used before Interrupts. In this method we constantly check the relevant software and hardware components for interrupts instead of getting signaled by them through interrupt signals.

Conclusion

Trap and Interrupt are two types of events. The trap is triggered by a user program to engage OS functionality, whereas the interrupt is triggered by a hardware device to allow the processor to execute the related interrupt handler method. This article describes the Difference between Trap and Interrupt in Operating System along with their working.

To better understand the topic, you can refer to Interrupt, Dual Mode Operations in OS, Clean Architecture and Introduction to Operating System.