Know and understand characteristics of ROM and RAM

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1. Types and Components of Computer Systems

1.1 Hardware and Software

Hardware – the physical parts of a computer (processor, memory chips, circuit boards, input & output devices, storage media).
Software – the set of instructions that tells the hardware what to do. It is divided into:

  • System software – operating systems, device drivers, firmware (e.g., BIOS/UEFI).
  • Application software – programmes that perform specific tasks for the user. Examples required by the Cambridge IGCSE syllabus:
    • Word processors
    • Web browsers
    • Database management systems (DBMS)
    • Video‑editing software

    Note: brand names (e.g., Microsoft Word, Adobe Premiere) are not scored – only the type of software matters.

1.2 Main Components of a Computer System

1.2.1 Central Processing Unit (CPU)

Aspect Details
Characteristic Executes program instructions by repeatedly performing the fetch‑decode‑execute cycle.
Key Parts Control Unit (directs operations), Arithmetic‑Logic Unit (performs calculations), Registers (very fast internal storage).
Uses Runs the operating system and all application programmes; performs calculations and logical decisions.
Advantages High processing speed; can execute billions of instructions per second (modern CPUs).
Disadvantages Consumes significant power and generates heat; performance limited by clock speed and architecture.

1.2.2 Internal Memory (ROM & RAM)

Read‑Only Memory (ROM)
Aspect Details
Characteristic Non‑volatile – data is retained when power is removed.
Writeability Read‑only in normal operation; some types can be rewritten only with special equipment (e.g., EPROM, EEPROM, Flash).
Typical Uses Firmware such as BIOS/UEFI, boot loaders, embedded controller code, permanent device drivers.
Advantages Data is permanent; provides a reliable place for essential system code.
Disadvantages Slower access than RAM; limited capacity; most types cannot be rewritten by the user.
Typical Capacity From a few kilobytes (micro‑controllers) to several megabytes (PC BIOS).
Common Types Mask ROM, PROM, EPROM, EEPROM, Flash ROM.
Random‑Access Memory (RAM)
Aspect Details
Characteristic Volatile – contents are lost when power is switched off.
Writeability Read/write; the CPU can modify data at any time.
Typical Uses Holds the operating system while it runs, active applications, temporary buffers, and cache.
Advantages Very fast access (nanosecond‑scale); allows rapid read/write operations needed for running programmes.
Disadvantages Data is lost on power‑off; more expensive per megabyte than secondary storage.
Typical Capacity From a few gigabytes in low‑end laptops to tens of gigabytes in high‑performance desktops; servers may use hundreds of GB.
Main Types Dynamic RAM (DRAM), Static RAM (SRAM), Synchronous DRAM (SDRAM), DDR‑x (DDR3, DDR4, DDR5) variants.
ROM vs RAM – Quick Comparison
Feature ROM RAM
VolatilityNon‑volatileVolatile
WriteabilityRead‑only or limited rewrite (EPROM, EEPROM)Read/write anytime
Primary purposeStore permanent firmware & boot codeProvide temporary workspace for programmes
SpeedSlower accessFast access (nanoseconds)
Typical capacityKB – MBGB – TB
ExamplesBIOS/UEFI, embedded controller firmware8 GB DDR4 module, 32 GB DDR5 module

1.2.3 Input / Output (I/O) Devices

Device Type Typical Use Key Characteristic Advantages Disadvantages
Keyboard Input Enter text and commands Low‑cost, tactile feedback Fast data entry, familiar layout Limited to text; not suitable for graphics input
Mouse / Touchpad Input Point, click, drag Precision control Accurate cursor movement, supports multiple buttons Requires a flat surface (mouse) or can be less precise (touchpad)
Monitor / Screen Output Display graphics & text Resolution & refresh rate Immediate visual feedback, supports colour Consumes power; size limited by desk space
Printer Output Produce hard‑copy documents Inkjet vs. laser, colour vs. monochrome Creates permanent records, useful for presentations Running cost (ink/toner), slower than screen display
Webcam / Microphone Input Capture video and audio Resolution, sampling rate Enables video conferencing, multimedia creation Quality varies; may raise privacy concerns

1.2.4 Backing (Secondary) Storage

Storage Type Typical Technology Typical Capacity Speed (Read/Write) Durability Advantages Disadvantages
Magnetic (HDD) Spinning platters, magnetic heads 0.5 TB – 10 TB (desktop) / 0.25 TB – 2 TB (laptop) ~80‑150 MB/s (varies with RPM) Mechanical parts → susceptible to shock High capacity for low cost, long‑standing technology Slower than SSD, noisy, higher power consumption
Solid‑State (SSD / Flash drive) NAND flash memory, no moving parts 128 GB – 8 TB 300‑3500 MB/s (NVMe) / 500‑600 MB/s (SATA) Resistant to shock, silent operation Very fast access, lower power use, lighter More expensive per GB, limited write‑cycles (though high in practice)
Optical (CD / DVD / Blu‑ray) Laser‑etched pits on plastic discs 700 MB (CD) – 100 GB (BD‑XL) ~5‑30 MB/s Read‑only (for most consumer media) → very stable Good for distribution, archival, low cost per disc Low capacity, slower, prone to scratches, largely obsolete for everyday use

All secondary storage is non‑volatile, retaining data when power is removed, but it is slower than RAM and is used for long‑term data keeping.

1.3 Operating Systems (OS)

An operating system is system software that manages hardware resources and provides a platform for application software.

Function Characteristic Uses Advantages Disadvantages
Memory Management Allocates and de‑allocates RAM to programmes Ensures each programme has its own workspace; supports multitasking Prevents programmes from interfering with each other Complex algorithms can add overhead
Process Scheduling Decides which programme (process) runs at any moment Enables multitasking and efficient CPU utilisation Responsive user experience Bad scheduling can cause lag or starvation of processes
File‑System Control Organises data on secondary storage (folders, permissions, indexing) Allows users and programmes to store, retrieve and protect files Provides a logical, hierarchical view of data Corruption or poor design can lead to data loss
User Interface (UI) Provides a way for users to interact with the computer (CLI or GUI) Command‑line for power users; graphical for most learners GUI is intuitive, reduces learning curve CLI requires memorisation of commands; GUI consumes more resources

Common OS families in the IGCSE syllabus

  • Windows – dominant desktop OS, GUI‑driven.
  • macOS – Apple’s desktop OS, strong multimedia support.
  • Linux – open‑source, highly configurable, often used on servers.
  • Android / iOS – mobile operating systems; touch‑screen oriented (included in the syllabus as “mobile OS”).

1.4 Types of Computers

Type Key Hardware Components Portability Expandability Typical Use‑Cases Advantages Disadvantages
Desktop PC CPU, 8‑64 GB RAM, HDD/SSD, separate graphics card Low (stationary) High – easy to add RAM, storage, expansion cards Office work, gaming, software development Powerful, upgradable, good cooling Bulky, needs external monitor/keyboard
Laptop / Notebook CPU, 4‑32 GB RAM, SSD/HDD, integrated graphics High (mobile) Medium – RAM/SSD upgrades often possible, limited slots Student work, travel, presentations Portable, all‑in‑one, battery powered Less powerful than desktops, limited upgrade options
Tablet System‑on‑Chip (CPU + GPU), 2‑8 GB RAM, flash storage Very high (hand‑held) Low – components soldered, storage not user‑replaceable Reading, web browsing, light apps Touch interface, lightweight, long battery life Limited multitasking, weaker hardware
Smartphone SoC, 4‑12 GB RAM, flash storage, integrated radios Very high Very low – virtually no user‑replaceable parts Communication, apps, media consumption Always with you, rich sensor suite Small screen, constrained processing power
All‑in‑One PC CPU, 8‑32 GB RAM, SSD/HDD, built‑in monitor Medium Medium – internal upgrades possible but space limited Space‑saving office setups, home media centre Compact, no separate tower Harder to service than a desktop, limited expansion

Regardless of form‑factor, every device contains ROM (firmware) and RAM (working memory) – the concepts are universal.

1.5 Analogue vs Digital Data

Analogue data is continuous (e.g., the varying voltage from a microphone).
Digital data is discrete, represented by binary numbers (0s and 1s). Computers can only process digital data, so conversion is required.

Analogue signal ──► ADC (Analogue‑to‑Digital Converter) ──► Digital data
                │                                          │
                ▼                                          ▼
          Processing (CPU, RAM)                         Storage
                │                                          │
                ▼                                          ▼
          Digital data ──► DAC (Digital‑to‑Analogue Converter) ──► Analogue output

1.6 Impact of Emerging Technologies

  • Artificial‑Intelligence (AI) accelerators – specialised chips (e.g., Tensor Processing Units) that rely on large, fast RAM buffers and firmware stored in ROM. Impact: dramatically increase processing speed for AI tasks but raise concerns about data privacy and energy consumption.
  • Extended Reality (XR) – VR/AR headsets – require high‑bandwidth RAM for real‑time rendering and ROM for device firmware. Impact: open new educational and entertainment experiences, yet demand powerful hardware and can cause motion‑sickness.
  • Internet of Things (IoT) devices – tiny micro‑controllers with flash ROM for firmware and a few kilobytes of RAM for sensor data. Impact: enable pervasive sensing and automation, but introduce security vulnerabilities and increase network traffic.
  • Edge computing – processes data close to the source (e.g., on a local server or smart camera) rather than in a distant cloud. Impact: reduces latency and bandwidth use, but requires distributed hardware with sufficient ROM and RAM at the edge.

1.7 Quick Quiz

  1. Which type of memory retains its data when the computer is switched off?
  2. Why is RAM described as volatile?
  3. List two types of ROM and give one example of where each is used.
  4. Explain why RAM is generally faster than ROM.
  5. Match the device to its category: Keyboard, SSD, Android OS, Tablet.

Answers

  • ROM (Read‑Only Memory).
  • Its cells store data as electrical charges that dissipate when power is removed (e.g., DRAM capacitors).
  • Mask ROM – used for fixed firmware such as early video‑game cartridges.
    EEPROM/Flash – used for BIOS/UEFI updates and firmware in smartphones.
  • RAM uses transistor‑based circuits optimised for rapid read/write cycles, whereas ROM cells are designed for permanence and therefore have slower access characteristics.
  • Keyboard – Input device; SSD – Backing storage; Android OS – Operating system (mobile); Tablet – Type of computer (mobile).

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