CH07-COA10e

Chapter 7: Input/Output

External Devices

  • Facilitate data exchange between external environment and computer.

  • Attach via a link to an I/O module used for control, status, and data exchange.

  • Peripheral Devices: External devices connected to I/O module.

    • Human Readable: Video display terminals, printers (communication with users).

    • Machine Readable: Magnetic disk/tape systems, sensors (communication with equipment).

    • Communication: Remote devices and other computers.

Block Diagram of External Device

  • Shows the structure of control signals and data transfer between I/O modules and external devices.

Keyboard/Monitor Interaction

  • Basic unit of exchange: Character.

    • Each represented by a unique 7-bit binary code; a total of 128 characters possible.

    • Two character types: Printable (e.g., letters, digits) and Control (commands for display).

  • Generates electronic signals interpreted by keyboard transducer.

Major Functions of I/O Module

  1. Control and Timing: Coordinates traffic between internal and external resources.

  2. Processor Communication: Command decoding, status reporting, and address recognition.

  3. Device Communication: Commands and data exchange with device.

  4. Data Buffering: Balances speeds of device and memory.

  5. Error Detection: Reports transmission errors.

I/O Techniques

  • Programmed I/O: Processor controls I/O operations directly. Can waste processor time.

  • Interrupt-Driven I/O: Processor can execute other instructions while waiting for I/O operations.

  • Direct Memory Access (DMA): Exchange of data between I/O module and memory without processor involvement.

I/O Commands

  • Types of commands: Control (activates devices), Test (checks status conditions), Read, Write (transmits data).

Hardware and Software Interrupts

  • Interrupt Processing: Handles interrupts from multiple devices and acknowledges requests.

  • Polling Techniques: Software poll, daisy chain, and bus arbitration for managing interrupts.

I/O Mapping

  • Memory-Mapped I/O: Shares address space with memory, allows read/write similar to memory commands.

  • Isolated I/O: Separate address spaces for devices.

Direct Memory Access (DMA) Basics

  • Addresses DMA architecture, including control logic, data transfer, and timing.

  • Differences in traditional DMA vs. newer strategies that reduce processor load.

I/O Peripheral Connection Technologies

  • Universal Serial Bus (USB): Dominant for peripheral connections with varying speeds.

  • FireWire: Alternative meant for high I/O rates.

  • SCSI: Once popular but less so now in smaller systems.

  • Thunderbolt: Latest technology offering high throughput.

  • InfiniBand: Targeted at high-end server markets.

  • Ethernet: Essential for networking, has evolved to accommodate 100 Gbps speeds.

  • Wi-Fi: Major wireless tech for devices; key for enhancing productivity.

Summary

  • I/O systems incorporate external devices, transfer protocols, direct memory access, and evolving connection technologies to manage data efficiently.