Know and understand the need to convert digital data to analogue data so it can be used to control devices

1. Types and Components of Computer Systems

1.1 Hardware & Software

• Hardware – the physical, tangible parts of a computer. Examples: CPU, RAM, motherboard, graphics card, network interface card, printer, scanner.
• Software – the set of instructions that tell the hardware what to do.

  • System software – manages hardware resources and provides a platform for other software.

    • Operating systems (e.g., Windows, macOS, Linux, Android, iOS)
    • Device drivers (software that allows the OS to communicate with a specific peripheral)
    • Utilities such as disk‑defragmenters, backup programmes, and firmware that controls embedded devices

  • Application software – performs particular tasks for the user.

    • Word processors, spreadsheets, web browsers, games, photo‑editing programmes

1.2 Main Components of a Computer System

How the components work together

The data path can be described as a simple flow:

1. The CPU fetches an instruction from RAM via the system bus.
2. The instruction may request data from an I/O device (e.g., read a key press) or from secondary storage (e.g., load a file).
3. Data moved between CPU, RAM and I/O devices is coordinated by controllers (memory controller, I/O controller) and the bus architecture.
4. When processing is complete, results are written back to RAM or stored permanently on the backing store.

A simple flow‑chart (textual) illustrates the cycle:

CPU → fetch instruction → RAM
↘︎ execute ↗︎
↘︎ read/write ↗︎
I/O controller ↔ peripheral
↘︎ store ↗︎
Secondary storage

1.3 Operating Systems

• Command‑Line Interface (CLI)

  • Example: MS‑DOS, Linux terminal
  • Advantage: fast for experienced users; uses very little system resources.
  • Disadvantage: steep learning curve; commands must be memorised.

• Graphical User Interface (GUI)

  • Example: Microsoft Windows, macOS, Ubuntu (Linux)
  • Advantage: intuitive – icons, windows and menus can be selected with a mouse or touch.
  • Disadvantage: consumes more memory and processing power than a CLI.

• Dialogue / Gesture‑Based Interface

  • Example: Android/iOS touch screens, Amazon Alexa voice control, Microsoft Kinect gestures
  • Advantage: natural interaction – useful for tablets, smartphones and some specialised equipment.
  • Disadvantage: can be less precise; may require additional hardware (touch sensor, microphone).

Modern operating systems often combine GUI with touch/gesture support (e.g., Windows 10 on a tablet).

1.4 Types of Computers

Why expandability matters (IGCSE context): Adding more RAM can allow larger spreadsheets or databases to be processed without slowing down; extra storage lets students keep more project files locally.

1.5 Emerging Technologies

• Artificial Intelligence (AI) – enables systems to learn from data.

  • Impact: personalised learning platforms can suggest resources tailored to a student’s progress.

• Extended Reality (XR) – Virtual Reality (VR) & Augmented Reality (AR)

  • Impact: immersive simulations for science labs or history field trips without leaving the classroom.

• Internet of Things (IoT) – everyday objects connected to the internet.

  • Impact: smart classroom sensors can automatically adjust lighting and temperature, improving comfort and energy use.

• Cloud Computing – on‑demand access to storage and processing over the internet.

  • Impact: students can store projects online and collaborate in real time without needing large local hard‑drives.

1.6 Analogue ↔ Digital Data Conversion

Why conversion is needed

• Physical limitation of many devices – actuators such as speakers, motors and LEDs respond to continuous voltage or current, not to discrete binary values.
• Human perception – our senses detect analogue phenomena (sound pressure, light intensity, temperature). To produce audible sound or visible light, digital data must be rendered as analogue signals.
• Compatibility with legacy equipment – many industrial control systems and older peripherals were designed before digital electronics became common.

Digital vs. Analogue – Quick Comparison

Digital‑to‑Analogue Converter (DAC)

A DAC receives a binary word and produces a proportional analogue voltage (or current).

Vout = Vref × D / 2ⁿ

• V_ref – reference voltage supplied to the DAC.
• D – decimal equivalent of the binary input word.
• n – number of bits of resolution (e.g., 8‑bit, 12‑bit, 16‑bit).
• More bits → smaller voltage steps → more accurate analogue reproduction.

Analogue‑to‑Digital Converter (ADC)

An ADC samples an analogue waveform at regular intervals and converts each sample into a binary value.

• Sampling frequency (Hz) – how often the signal is measured. By the Nyquist theorem it must be at least twice the highest frequency component of the signal.
• Resolution (bits) – determines how many discrete levels are available; a 10‑bit ADC gives 2¹⁰ = 1024 levels.
• Quantisation error – the difference between the true analogue value and the nearest representable digital level.

Practical examples of conversion

1. Audio playback – a digital audio file (MP3, WAV) is sent to a DAC; the resulting varying voltage drives a speaker diaphragm to produce sound.
2. Motor speed control – a microcontroller outputs a Pulse‑Width Modulated (PWM) signal; after simple filtering the PWM becomes a smooth analogue voltage that sets the motor’s supply voltage.
3. Display brightness – graphics data are converted by a DAC into analogue voltage levels that control the intensity of an LCD backlight or OLED pixel current.
4. Digital photograph → analogue print – the image data stored digitally are converted by a DAC inside a printer to analogue voltage pulses that drive the print head, producing a physical photograph.

Process flow – converting digital data to an analogue signal

1. Generate the binary word that represents the desired output (e.g., one audio sample).
2. Send the word to a DAC.
3. The DAC produces a stepped analogue voltage proportional to the binary value.
4. If a smooth waveform is required, the stepped output is passed through a simple low‑pass filter (removes the high‑frequency “steps”).
5. The filtered analogue signal drives the target device – speaker, motor, LED, printer head, etc.

1.7 Summary

• Computer systems consist of hardware (CPU, memory, I/O, storage) and software (system & application).
• The CPU fetches instructions from RAM, works with I/O controllers and stores results on secondary storage via the system bus.
• Operating systems provide three interface styles – CLI, GUI and dialogue/gesture – each with its own strengths and weaknesses.
• Different computer categories balance portability against expandability; expandability is important for tasks such as adding RAM for larger spreadsheets.
• Emerging technologies (AI, XR, IoT, Cloud) are already influencing everyday ICT use in classrooms and homes.
• Many external devices need analogue signals; conversion is achieved with DACs (digital → analogue) and ADCs (analogue → digital). Understanding why conversion is required and how the converters work is essential for designing, using and troubleshooting ICT systems that interact with the physical world.