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Modes of transfer, interrupts, and interrupt handling are crucial concepts in computer architecture and operating systems. They are fundamental to managing communication between the CPU and I/O devices efficiently. Let’s explore each in detail:

Modes of Transfer:

  1. Programmed I/O (PIO):
    • In PIO, the CPU directly controls data transfer between the I/O device and memory.
    • The CPU initiates data transfers by polling the device or waiting for status signals.
    • Suitable for low-speed devices and simple I/O operations but can result in high CPU overhead and inefficient use of resources.
  2. Interrupt-Driven I/O:
    • In interrupt-driven I/O, the CPU is freed from continuously polling devices by responding to interrupts generated by the devices.
    • Devices signal the CPU when they need attention or when data transfer is complete.
    • Allows the CPU to perform other tasks while waiting for I/O operations to complete, improving system efficiency.
    • More complex to implement but provides better performance and resource utilization compared to PIO.
  3. Direct Memory Access (DMA):
    • DMA allows devices to transfer data directly to and from memory without CPU intervention.
    • A DMA controller manages the data transfer, allowing the CPU to perform other tasks concurrently.
    • Ideal for high-speed data transfer between devices and memory, reducing CPU overhead and improving system throughput.

Interrupts & Interrupt Handling:

  1. Interrupts:
    • Interrupts are signals generated by hardware devices to request attention from the CPU.
    • Interrupts can be triggered by various events, such as I/O completion, hardware errors, timer expiration, or external user input.
    • Upon receiving an interrupt, the CPU suspends its current execution and transfers control to an interrupt handler, also known as an interrupt service routine (ISR).
  2. Interrupt Vector Table (IVT):
    • The interrupt vector table is a data structure used by the operating system to map interrupt numbers to their corresponding interrupt handlers.
    • Each entry in the IVT contains the address of the interrupt handler for a specific interrupt number.
  3. Interrupt Handling Process:
    • When an interrupt occurs, the CPU saves its current state (program counter, registers) and transfers control to the interrupt handler associated with the interrupt number.
    • The interrupt handler executes the necessary tasks to service the interrupt, such as handling I/O operations, updating system state, or processing data.
    • After completing the interrupt handler, the CPU restores its previous state and resumes execution of the interrupted program.
  4. Interrupt Priority:
    • Some systems support multiple interrupt sources with varying priority levels.
    • Interrupt priority determines the order in which interrupts are serviced when multiple interrupts occur simultaneously.
    • Higher-priority interrupts preempt lower-priority interrupts, ensuring that critical tasks are handled promptly.

Effective interrupt handling is essential for efficient I/O operations, real-time processing, and overall system responsiveness. It allows the CPU to manage multiple tasks concurrently while efficiently servicing I/O requests from various devices.