Know and understand the role of the CPU in processing instructions entered into the computer in order to produce an output

Learning Objective

Know and understand the role of the Central Processing Unit (CPU) in processing instructions entered into the computer in order to produce an output, and be able to relate this to the wider ICT system described in the Cambridge IGCSE (0417) syllabus.

1. Overview of Computer Systems

1.1 Hardware and Software

• Hardware – the physical components of a computer (CPU, memory, storage, input & output devices, networking equipment).
• Software – programmes that tell the hardware what to do.

  • System software – operating system (OS), device drivers, utility programmes. It manages resources and provides a platform for applications.
  • Application software – word processors, spreadsheets, databases, web browsers, games, specialist apps (e.g., school‑management, banking, medical).

1.2 Analogue vs Digital Data

• Analogue data – continuous signals (e.g., sound waves, light intensity). Represented by varying voltage or current.
• Digital data – discrete binary values (0 or 1). Used by computers because it is less susceptible to noise.
• Conversion is required for most interactions:

  • Analogue‑to‑Digital Converter (ADC) – microphone, scanner, camera.
  • Digital‑to‑Analogue Converter (DAC) – speakers, printer head, display.

2. Main Components of a Computer System

3. Operating Systems (OS)

The OS manages hardware resources, provides a user interface and a platform for application software.

4. Types of Computer Systems

5. Input and Output Devices

5.1 Input Devices

5.2 Output Devices

6. Storage Devices & Media

6.1 Comparative Matrix

6.2 Backup & Archival Media

• External HDD/SSD – convenient for regular user backups.
• Magnetic tape (LTO) – high capacity, used by businesses for long‑term archival.
• Cloud storage – remote servers accessed via the Internet; offers automatic backup and off‑site safety.

7. Networks & Effects of Using IT

7.1 Types of Networks

• LAN (Local Area Network) – connects devices within a building or campus; high speed (Ethernet or Wi‑Fi).
• WLAN (Wireless LAN) – Wi‑Fi implementation of a LAN; provides mobility.
• WAN (Wide Area Network) – spans cities, countries or continents; uses leased lines, satellite, or the Internet.
• Internet – global WAN that interconnects millions of private, public, academic and business networks.
• Intranet – private network using Internet protocols, restricted to an organisation.
• Extranet – part of an intranet made accessible to external partners or customers.

7.2 Network Hardware (Key Components)

• Router – stores IP addresses, determines the best path for data packets, and forwards them between different networks (e.g., LAN ↔ Internet).
• Switch – connects multiple devices within a LAN; forwards frames based on MAC addresses.
• Network Interface Card (NIC) – provides a physical connection (wired or wireless) for a device to join a network.
• Access Point (AP) – creates a WLAN by linking wireless devices to a wired LAN.
• Modem – converts digital data to analogue (and vice‑versa) for transmission over telephone, cable or DSL lines.

7.3 Cloud Computing

Cloud computing delivers IT services (storage, processing power, applications) over the Internet.

• Advantages: scalability, pay‑as‑you‑go, accessibility from any device with Internet.
• Disadvantages: reliance on Internet connectivity, ongoing subscription costs, data‑privacy and security concerns.

7.4 Security Considerations

• Password hygiene – strong, unique passwords; regular changes; two‑factor authentication.
• Anti‑malware software – scans for viruses, worms, ransomware; keeps definitions up‑to‑date.
• Firewalls – hardware or software that controls traffic based on defined rules.
• Encryption – protects data in transit (HTTPS, VPN) and at rest.
• Backup & recovery – regular backups to local or cloud media to mitigate data loss.

7.5 Effects of Using IT

• Health issues – repetitive‑strain injury (RSI), back and neck pain, eye strain, headaches. Preventive strategies: ergonomic workstation, regular breaks, proper lighting.
• Micro‑processor‑controlled devices – smart homes, autonomous vehicles, wearable fitness trackers. Social/ethical impacts include privacy concerns, data ownership, and the digital divide.
• Emerging technologies – AI (voice assistants, image recognition), XR (virtual/augmented reality), IoT (networked sensors). These broaden the range of applications but also raise ethical questions about bias, surveillance, and environmental impact.

8. ICT Applications (Communication, Modelling, Specialist Systems)

• Communication – email, instant messaging, video‑conferencing (Zoom, Teams), social media, collaborative platforms.
• Modelling & Simulation – spreadsheets for financial modelling, CAD for engineering design, GIS for geographic modelling, physics/chemistry simulation software.
• Specialist Applications:

  • School‑management systems – timetabling, attendance, grading.
  • Booking & reservation systems – travel, hotels, event tickets.
  • Banking systems – account management, online payments, ATMs.
  • Medical information systems – patient records, diagnostic imaging.
  • Retail point‑of‑sale (POS) systems – inventory, sales reporting.
  • Expert systems – rule‑based decision support (e.g., medical diagnosis).
  • Recognition systems – facial, fingerprint, voice recognition.
  • Satellite systems – GPS navigation, weather monitoring, communications.

9. The Central Processing Unit (CPU)

9.1 Role of the CPU

• Executes the instructions of a programme (the fetch‑decode‑execute cycle).
• Controls the flow of data between memory, input, output and storage via the system bus.
• Performs arithmetic and logical operations using the Arithmetic Logic Unit (ALU).
• Coordinates multiple cores/threads to allow parallel processing.

9.2 The Instruction Cycle (Fetch‑Decode‑Execute)

1. Fetch – The Program Counter (PC) points to the next instruction in RAM; the instruction is copied into the Instruction Register (IR).
2. Decode – The Control Unit interprets the opcode, determines which operation the ALU must perform, and identifies any required operands.
3. Execute – The ALU carries out the operation (e.g., addition, comparison); results may be stored in a register or written back to RAM.
4. After execution, the PC is updated (usually incremented) and the cycle repeats until a halt or interrupt occurs.

9.3 CPU Components

• Control Unit (CU) – Generates control signals, manages the instruction cycle.
• Arithmetic Logic Unit (ALU) – Performs arithmetic (add, subtract) and logical (AND, OR, NOT) operations.
• Registers – Small, fast storage inside the CPU (e.g., accumulator, program counter, instruction register).
• Cache memory – Very fast memory (L1, L2, L3) that stores frequently used instructions/data to speed up processing.

9.4 From Input to Output – A Simple Example

1. User presses “5” on the keyboard (input device).
2. Keyboard controller converts the key‑press into a binary scan code and sends it via the system bus to RAM.
3. The operating system loads the calculator programme into RAM; the CPU fetches the first instruction.
4. CPU decodes the instruction “store scan code in register A”.
5. User presses “+”; the same cycle repeats, now performing an addition operation in the ALU.
6. Result (e.g., “8”) is placed in a register, written back to RAM, and finally sent to the monitor via the graphics controller – the output is displayed.

10. Systems Development Life‑Cycle (SDLC)

The SDLC provides a structured approach to creating or modifying ICT systems.

1. Analysis – Identify user requirements, define the problem.
2. Design – Plan system architecture, data flow diagrams, UI mock‑ups.
3. Development / Programming – Write and compile code.
4. Testing – Verify functionality, debug, perform user acceptance testing.
5. Implementation – Deploy the system, train users, migrate data.
6. Maintenance – Ongoing updates, security patches, performance monitoring.

11. Summary

• The CPU is the “brain” that carries out the fetch‑decode‑execute cycle, turning user input into meaningful output.
• Hardware and software work together; system software manages resources while application software performs specific tasks.
• Understanding analogue‑digital conversion, direct‑data‑entry devices, storage media, networks, and the effects of IT use is essential for the IGCSE ICT syllabus.
• Awareness of health, ethical and societal impacts, as well as emerging technologies, prepares students for responsible use of ICT.
• Applying the SDLC ensures that ICT solutions are developed systematically and meet user needs.