LESSON 2: INPUT / OUTPUT TECHNOLOGY

External devices

Hardware components that let a computer communicate with the outside world or store data outside main memory.

Human-readable devices

External devices that provide communication between the user and computer, such as a keyboard, mouse, display, or printer.

Machine-readable devices

External devices that exchange data directly with equipment or storage systems, such as sensors, actuators, or disks.

Communication devices

Devices that transfer data between computers or communication systems, such as a network interface, modem, or wireless adapter.

Input device

A device that converts information from a user or the environment into signals a computer can process.

Output device

A device that converts computer-generated information into a form understood by a person or used by another machine.

Storage device

A device that transfers blocks of data between the computer and secondary storage.

I/O (Input/Output) module

An interface between the processor/memory system and external devices that provides control and coordination.

Control and timing

An I/O module function that coordinates the sequence of input/output operations.

Processor communication

An I/O module function that receives commands and exchanges data or status information with the CPU.

Device communication

An I/O module function that sends control signals to and receives signals from an external device.

Data buffering

Temporarily holding data to compensate for speed differences between components.

Error detection (I/O)

An I/O module function that reports device or data-transfer errors to the processor.

Data register

An I/O module register that holds data being transferred between the module and the processor/device.

Status register

An I/O module register that indicates conditions such as ready, busy, completed, or error.

Control register

An I/O module register that receives commands controlling the I/O operation.

Programmed I/O

A data-transfer method controlled directly by the CPU, which repeatedly checks the device status until it is ready.

Polling

Repeatedly checking a device’s status to determine whether it is ready or the operation is complete.

Interrupt-driven I/O

A method that lets the CPU do other work while a device operates; the I/O module interrupts the CPU when service is needed.

Interrupt request

A signal from an I/O module asking the CPU for attention or service.

Interrupt service routine

The routine the CPU executes to handle an interrupt.

Direct Memory Access (DMA)

A method in which a DMA controller transfers blocks of data directly between an I/O device and main memory with limited CPU involvement.

DMA controller

Hardware that manages direct data transfers between an I/O device and main memory.

Burst / block DMA

A DMA mode that transfers a block of data in one continuous sequence before returning bus control.

Cycle stealing

A DMA mode in which DMA takes individual bus cycles from the CPU to transfer data.

Transparent DMA

A DMA mode that transfers data when the CPU is not using the bus, minimizing interference with CPU activity.

I/O channel

A specialized mechanism that can execute I/O-related instructions and manage transfers independently of the main CPU.

I/O processor (IOP)

A dedicated processor for controlling I/O operations, coordinating devices, and managing transfers with less direct CPU involvement.

System throughput

The overall amount of work or data a system can process in a given time.