Describe the principal operations of hardware devices

3.1 Computers and Their Components

Objective

Describe the principal operations of hardware devices.

1. Central Processing Unit (CPU)

The CPU is the brain of the computer. Its main operations are:

• Fetch – Retrieve the next instruction from memory.
• Decode – Interpret the instruction and determine the required action.
• Execute – Perform the operation (e.g., arithmetic, logical, data movement).
• Store – Write the result back to a register or memory location.

The speed of these operations is often expressed by the clock period \$T\$:

\$T = \frac{1}{f}\$

where \$f\$ is the clock frequency (in Hz).

2. Memory Devices

Memory stores data and instructions. Its principal operations are:

• Read – Transfer data from a memory location to the CPU.
• Write – Transfer data from the CPU to a memory location.
• Refresh (for DRAM) – Periodically rewrite stored charge to prevent loss.

3. Input Devices

Input devices convert physical signals into digital data that the CPU can process.

4. Output Devices

Output devices transform digital data into human‑readable or usable forms.

5. Storage Devices

Storage devices retain data when the computer is powered off. Their key operations include:

• Sequential Access – Data is read/written in a fixed order (e.g., magnetic tape).
• Random Access – Data can be read/written at any location directly (e.g., HDD, SSD).
• Erase/Write Cycle – For flash memory, each block must be erased before being rewritten.

6. Bus and Control Unit

The bus provides pathways for data, addresses, and control signals. Its operations are:

1. Transfer data between CPU, memory, and I/O devices.
2. Carry address information to specify the source or destination.
3. Transmit control signals (read/write, interrupt, clock) to coordinate activity.

7. Summary of Principal Operations