Input/Output Devices and Interfaces

This lesson covers how the processor communicates with peripheral devices — keyboards, displays, storage, sensors, and more. At A-Level you must understand I/O techniques, the role of device drivers, and how data is transferred between the CPU and peripherals.

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I/O Ports and Device Controllers

Every peripheral device connects to the CPU through an I/O port managed by a device controller (or I/O controller). The device controller:

• Translates between the device's own signalling format and the system bus format.
• Contains its own small set of registers (status register, control register, data register).
• Communicates with the CPU via the system bus.

┌─────┐     ┌──────────────┐     ┌──────────────┐
│ CPU │ ──→ │ Device       │ ──→ │ Peripheral   │
│     │ ←── │ Controller   │ ←── │ Device       │
└─────┘     └──────────────┘     └──────────────┘
         System Bus          Device-specific signals

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Methods of I/O Data Transfer

1. Programmed I/O (Polling)

The CPU continuously checks (polls) the device's status register to see if data is available or if the device is ready.