Notes on Input-Output Structure in Operating Systems

Overview

• Previous Topic: Storage Structure in Operating Systems
• Current Topic: Input-Output (I/O) Structure in Operating Systems

Input-Output Devices

• Definition: Devices that provide input to or receive output from a computer.
• Importance:
  • Essential for system reliability and performance.
  • Large portion of OS code is dedicated to managing I/O due to the varying nature of devices.

Computer System Components

• General Purpose Computer:
  • Contains one or more CPUs.
  • Multiple device controllers connected through a common bus.
  • Shared memory access provided by the common bus.

Device Controllers

• Each device controller manages a specific type of device (e.g., disk controllers, USB controllers).
• Responsibilities:
  • Maintains a local buffer storage.
  • Maintains a set of special purpose registers.

Device Drivers

• Definition: Software that interfaces between device controllers and the OS.
• Function:
  • Understands the device controller's operation.
  • Presents a uniform interface to the rest of the operating system.

Basic I/O Operation Process

1. Load Registers: Device driver loads appropriate registers in the device controller.
2. Examine Registers: Device controller examines registers to determine the necessary action.
3. Data Transfer: Controller transfers data from the device to its local buffer.
4. Completion Notification: Device controller sends an interrupt to inform the device driver that the operation is complete.
5. Return Control: Device driver returns control back to the operating system.

Diagram of I/O Operation

• Representation of the I/O operation process, highlighting:
  • Interaction between CPU, device, and memory.
  • Data transfer and control flow.

Disadvantages of Interrupt Driven I/O

• Efficiency Issues:
  • Suitable for small data transfers.
  • High overhead for bulk data movement due to frequent interrupts.

Direct Memory Access (DMA)

• Purpose: To improve efficiency for bulk data transfers.
• Process:
  1. Setup buffers, pointers, and counters for I/O devices.
  2. Device controller transfers data directly between its buffer and memory, bypassing the CPU.
  3. Only one interrupt per block is generated to signal completion.
• Advantages:
  • CPU remains free to perform other tasks during I/O operations.
  • Reduces the number of interrupts, improving performance.

Conclusion

• Understanding I/O structure is vital for operating system performance and reliability.
• The lecture covered the functioning of I/O operations and the advantages of DMA.