Hardware interrupts are generated by external devices to signal the CPU that they require attention. They are triggered by physical events, such as a key press, a network packet arrival, or a disk read completion. They are typically faster than software interrupts because they are directly triggered by hardware.

Example of a hardware interrupt: A keyboard press. When you press a key, the keyboard controller sends a hardware interrupt signal to the CPU. The CPU then executes the interrupt handler to determine which key was pressed and takes appropriate action.

Software interrupts are generated by instructions within a program. They are used to request services from the operating system, such as file I/O or system calls. They are slower than hardware interrupts because they involve a context switch to the operating system kernel.

Example of a software interrupt: A program using the INT instruction to request a file to be opened. This triggers a software interrupt, transferring control to the operating system's kernel, which then handles the file opening request.

To run application software, a computer relies on the coordinated interaction of hardware, firmware, and an operating system. Each plays a distinct and crucial role:

• Hardware: This refers to the physical components of the computer system, such as the CPU, memory (RAM), storage devices (hard drive/SSD), and input/output devices. Hardware provides the physical platform upon which all other components operate. It executes instructions and stores data. Without hardware, there is nothing to execute the software.
• Firmware: Firmware is a type of software that is embedded directly into hardware devices. It's typically stored in non-volatile memory (like ROM or flash memory) and provides low-level control for the hardware. Examples include the BIOS/UEFI in the motherboard, which initializes the hardware during the boot process, and the firmware in devices like hard drives or printers. Firmware is essential for the hardware to function correctly and is often the first software to run when the computer is powered on.
• Operating System (OS): The OS is a system software that manages computer hardware and software resources. It acts as an intermediary between the application software and the hardware. The OS provides essential services to applications, including memory management, process scheduling, file system management, and device drivers. The OS loads the application software into memory, allocates resources to it, and provides a platform for the application to execute. Without an OS, applications would not be able to interact with the hardware or each other.

In essence, the hardware provides the physical machinery, the firmware enables the hardware to start and function, and the operating system provides the environment and services necessary for applications to run.

Interrupts are signals that cause the CPU to temporarily stop its current task and execute a specific routine, known as an interrupt handler. Their primary role is to allow the system to respond to events, both internal (e.g., a device requesting attention) and external (e.g., a user pressing a key). Without interrupts, the CPU would have to constantly poll devices to check for activity, which is inefficient.

The handling of an interrupt typically involves the following steps:

• Interrupt Request (IRQ): A device sends an IRQ signal to the CPU.
• Interrupt Recognition: The CPU checks if it is currently in a critical section (e.g., performing a time-critical operation) and whether interrupts are enabled.
• Interrupt Disable (Optional): If the interrupt is not to be serviced immediately, the CPU may disable interrupts temporarily.
• Save Context: The CPU saves the current state of the program (registers, program counter) onto the stack. This allows the CPU to resume the interrupted program later.
• Interrupt Vector: The CPU uses the IRQ signal to determine the address of the appropriate interrupt handler in the interrupt vector table.
• Jump to Handler: The CPU jumps to the address specified in the interrupt vector table, executing the interrupt handler.
• Service the Request: The interrupt handler performs the necessary actions to respond to the event that caused the interrupt (e.g., reading data from a device).
• Restore Context: The CPU restores the saved context from the stack.
• Interrupt Enable: The CPU re-enables interrupts (if they were disabled).
• Return to Program: The CPU returns to the point where it was interrupted and resumes execution.