Computer System Components: I/O, Buses & Peripherals Explained

Input/Output (I/O) Units

I/O units connect the system to the outside world, enabling the introduction and extraction of information. These units typically consist of registers operated by control buses, storing address information from the data bus. Their outputs are externally accessible for connecting to various devices.

Another crucial function of I/O units is to adapt:

• The format of signals from outside to the format of internal signals.
• Working speeds.
• Voltage levels.
• Binary codes.

System Buses

All elements of a programmable microsystem are interconnected by information channels, commonly known as buses. These buses are composed of multiple lines, each designed to transmit information of a specific type. The number of lines forming a bus determines its width. For example, a 16-bit data bus signifies that 16 bits of data can circulate in parallel simultaneously.

Data Bus

The data bus carries the bits that constitute binary information, instructions, or data stored in memory locations or registers. Its width corresponds to the data word size with which the system operates. For instance, an 8-bit microprocessor typically has an 8-wire data bus.

This bus is bidirectional, allowing devices to both receive information (write operations) and send information (read operations), depending on the state of the control bus's read/write line. Data bus lines are commonly labeled with the initial D (for Data).

Address Bus

The address bus transmits the bits that select specific memory locations or I/O devices for read or write operations. The number of lines (conductors) in this bus corresponds to the number of address bits the system uses. The width of the address bus determines the maximum amount of memory the system can address.

The maximum number of addresses is calculated as 2ⁿ, where 'n' is the number of address bus lines. This bus is unidirectional; its lines transmit information in only one direction, with the control unit being the sole component that can utilize it. Address bus lines are typically referred to by the initial A (for Address).

Control Bus

The control bus comprises a series of lines that transmit all necessary signals for the proper coordination of all system elements. These signals include read/write orders, device enable/disable signals, interrupt requests, and other synchronization signals.

Peripherals

Peripherals encompass a wide range of devices, circuits, and machines – essentially, all external devices controlled by the system that perform specific tasks. Peripherals are typically classified by their function:

• Communication Peripherals: These devices facilitate the exchange of information between the system and the outside world. They send information from inside the system outwards (output) or receive information from external sources (input).
• Mass Storage Peripherals: These devices are designed to store large amounts of information permanently and securely, even when power is off.