Describe the principal operations of hardware devices

3.1 Computers and Their Components

CPU – The Brain 🧠

The CPU carries out the fetch‑decode‑execute cycle:

  1. Fetch – Retrieve instruction from memory.
  2. Decode – Translate instruction into control signals.
  3. Execute – Perform the operation (arithmetic, logic, data movement).

Clock speed determines how many cycles per second: $f$ (Hz). The period is $t = \frac{1}{f}$.

Exam Tip: Remember the order: Fetch → Decode → Execute. Many questions ask you to identify which part of the CPU handles a specific task.

Memory – Short‑Term & Long‑Term 📚

Type Speed (approx.) Capacity Volatility
Registers Fastest Few KB Volatile
Cache (L1/L2/L3) Very fast Up to MB Volatile
RAM Fast GBs Volatile
SSD/HDD Slowest TBs Non‑volatile
Exam Tip: When asked to choose the fastest memory for a specific task, think Registers > Cache > RAM > SSD/HDD.

I/O Devices – The Ears & Mouth 📡

  • Input – Keyboard, mouse, microphone, sensors.
  • Output – Monitor, printer, speaker, actuators.
  • Storage (secondary) – SSD, HDD, USB drives.

Data flows via bus interfaces (e.g., USB, PCIe). The CPU sends a command; the device returns data.

Exam Tip: Identify whether a device is input or output by its role in the data flow diagram.

Bus & Interconnects – The Road Network 🚗

Bus Type Purpose Bandwidth (approx.)
System Bus (CPU‑RAM) Core data transfer Gbps
Peripheral Bus (USB, PCIe) Device connectivity Gbps to Tbps
Internal Bus (Cache‑CPU) Fast cache access Tps
Exam Tip: When a question mentions “high bandwidth”, think of PCIe or NVMe; for “low latency”, think of the system bus.

Power Supply – The Energy Source ⚡

Converts mains AC to low‑voltage DC for components. Typical voltages:

  • CPU: 1.2 V – 1.5 V
  • RAM: 1.5 V – 1.35 V
  • GPU: 1.0 V – 1.2 V
  • Motherboard: 3.3 V, 5 V, 12 V

Power factor and efficiency (usually 80 %+). Surge protection protects against spikes.

Exam Tip: If a question asks about “voltage regulation”, recall the role of the voltage regulator module (VRM) on the motherboard.

Key Takeaways for the Exam

  • Remember the CPU cycle: Fetch → Decode → Execute.
  • Memory hierarchy: Registers > Cache > RAM > SSD/HDD.
  • Input devices bring data into the computer; output devices send data out of the computer.
  • Bus types differ in purpose and bandwidth; match the right bus to the right device.
  • Power supply must provide correct voltages and protect against spikes.

Good luck, and remember to diagram the data flow whenever possible – diagrams often earn extra marks!

Revision

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