L26_Ch11a

Chapter 11: I/O Management and Disk Scheduling

General Information

• Ninth Edition, Global Edition by William Stallings

• Copyright © 2018 Pearson Education, Ltd. All Rights Reserved.

11.1 I/O Design

I/O Device Categories

• Human-readable devices: Communication with computer users.

  • Examples: Printers, terminals, video displays, keyboards, mice.

• Machine-readable devices: Communication with electronic equipment.

  • Examples: Disk drives, USB keys, sensors, controllers.

• Communication devices: Interaction with remote devices.

  • Examples: Modems, digital line drivers.

11.2 Device Characteristics

• Data Rate: Differences in data transfer rates among devices.

• Application: Influence of device use on software and processes.

• Complexity of Control: Impact on operating system management based on I/O module complexity.

• Unit of Transfer: Bytes, characters, or larger blocks can be transferred.

• Data Representation: Various encoding schemes may be utilized.

• Error Conditions: Devices have different error reporting and response mechanisms.

11.3 I/O Techniques

Techniques for Performing I/O

1. Programmed I/O: Processor waits for I/O operation completion after issuing a command.

2. Interrupt-driven I/O:

   • Non-blocking mode: Processor continues with other tasks after issuing I/O command.

   • Blocking mode: Processor halts current task, puts it in a blocked state until the I/O complete.

3. Direct Memory Access (DMA): DMA module manages data exchanges between main memory and I/O modules.

Alternative DMA Configurations

• Various configurations for integrating DMA to enhance data transfer efficiency.

Efficiency and Generality in I/O Design

• Efficiency: Critical since I/O operations can bottleneck performance; slow compared to CPU and memory speeds.

• Generality: Need for uniform handling of diverse devices; hierarchical and modular design approaches are encouraged.

Design Objectives

• Separation of operating system functions based on complexity and abstraction levels leads to layered OS design.

11.3 I/O Buffering

Buffering Techniques

1. Single Buffering: A single buffer in memory to process I/O; can result in speedup but complicates logic.

2. Double Buffering: Two buffers allow for overlapping operations: one buffer is processed while the other is filled.

3. Circular Buffering: Multiple buffers utilized in a circular configuration, solving issues where I/O must match processing pace.

Summary of Buffering Methods

• Single Buffer: Basic buffering.

• Double Buffer: Increased efficiency through simultaneous operations.

• Circular Buffer: Keeps process continuous without interruption, adjusting for I/O peaks.

Conclusion

• Understanding I/O management and disk scheduling is essential for optimizing computer system performance, addressing factors like buffering, I/O techniques, and device characteristics to improve overall system efficiency.