Hardware

Computers and their components.

Input: are hardware components that allow users to enter data and instructions into a computer system.

Reason	Explanation	Example
User interaction	Allows humans to communicate with the computer	Keyboard, mouse, touchscreen
Data entry	Enables entering raw data for processing	Scanner, barcode reader, microphone
Control	Allows users to give commands and instructions	Mouse clicks, keyboard shortcuts
Environment sensing	Captures data from the physical world	Sensors, cameras, temperature probes
Authentication	Verifies user identity	Fingerprint scanner, iris scanner

Output: are hardware components that present processed data to the user in a human-readable or usable form.

Reason	Explanation	Example
User feedback	Shows results of processing to the user	Monitor, speakers
Data persistence	Creates physical copies of information	Printer, plotter
Communication	Presents information for decision-making	Display screens, projectors
Control signals	Controls external devices/machines	Actuators, motors (robotics)
Visualisation	Displays complex data in understandable formats	Graphs, charts on screen

NEED FOR PRIMARY MEMORY

Primary memory (also called main memory) is the fast, volatile memory directly accessible by the CPU.

It includes RAM (Random Access Memory) and ROM (Read-Only Memory).

Reason	Explanation	Example
Program storage	Stores the currently running programs and operating system	RAM holds OS and running applications
Data storage	Stores active data being processed	Variables, input data, intermediate results
Speed	Much faster than secondary storage — enables CPU to operate at full speed	DDR4 RAM: ~20 GB/s vs HDD: ~0.1 GB/s
Direct CPU access	CPU can read/write directly from primary memory	Via memory bus, no mechanical delays
Temporary workspace	Provides a workspace for the CPU during processing	Scratchpad for calculations

RAM (Random Access Memory)

Feature	Description
Volatile	Data lost when power is removed
Read/Write	Can read and write data
Speed	Very fast (nanoseconds access time)
Purpose	Holds programs and data currently in use
Size	Typically 4GB – 128GB in modern computers

ROM (Read-Only Memory)

Feature	Description
Non-volatile	Data retained when power is removed
Read-only	Cannot be modified (or only with special hardware)
Speed	Fast (slower than RAM but faster than secondary storage)
Purpose	Stores boot-up instructions (BIOS/UEFI)
Size	Typically 2MB – 64MB

SECONDARY STORAGE

Secondary storage (also called backing storage) is non-volatile storage used for permanent retention of data and programs.

It includes hard disk drives (HDD), solid-state drives (SSD), and removable media.

Reason	Explanation	Example
Permanent storage	Retains data and programs when power is removed	Operating system, documents, photos
Large capacity	Much larger capacity than primary memory	Terabytes of data storage
Cost-effective	Much cheaper per GB than primary memory	HDD: ~£0.03/GB vs RAM: ~£6/GB
Backup and archive	Preserves data for long-term storage	Backups, archives, historical records
Transfer of data	Allows data transfer between computers	USB drives, external HDDs

REMOVABLE STORAGE

Removable storage is a type of secondary storage that can be physically removed from the computer and transported to another device.

Why is Removable Storage Needed?

Reason	Explanation	Example
Data portability	Transfer data between different computers	USB flash drives, external drives
Offline backup	Create backups that are physically separate from the computer	External hard drives
Distribution	Distribute software, media, or files to others	CDs, DVDs, USB drives
Disaster recovery	Store critical data offsite for disaster recovery	Tape backups
Limited connectivity	Transfer data when network access is unavailable	USB drives

Comparison Table (Exam Revision)

Feature	Input	Output	Primary Memory	Secondary Storage	Removable Storage
Purpose	Enter data	Present results	Temporary storage	Permanent storage	Portable storage
Examples	Keyboard, mouse	Monitor, printer	RAM, ROM, Cache	HDD, SSD	USB drive, CD
Volatility	N/A	N/A	Volatile (RAM) / Non-volatile (ROM)	Non-volatile	Non-volatile
Speed	Depends on device	Depends on device	Very fast	Slow	Slow
Capacity	N/A	N/A	Small (GBs)	Large (TBs)	Varies (MBs – TBs)
CPU access	CPU cannot access directly	CPU cannot access directly	Direct access	Indirect access	Indirect access

The Data Flow: How Components Work Together

text

                    USER
                      │
            ┌─────────┴─────────┐
            ▼                   ▼
     ┌─────────────┐     ┌─────────────┐
     │  INPUT       │     │  OUTPUT     │
     │  (Keyboard)  │     │  (Monitor)  │
     └──────┬──────┘     └──────┬──────┘
            │                   ▲
            ▼                   │
     ┌──────────────────────────────┐
     │        PRIMARY MEMORY         │
     │      (RAM / ROM / Cache)      │
     │       - Holds active data     │
     │       - Fast access           │
     └──────────┬───────────┬────────┘
                │           │
                ▼           ▼
         ┌─────────────┐   ┌──────────────────┐
         │     CPU     │   │   SECONDARY      │
         │  (Process)  │   │   STORAGE        │
         └─────────────┘   │   - Permanent    │
                           │   - Large capacity│
                           │   - Slow access  │
                           └──────────────────┘

Common Exam Mistakes

Mistake	Correct
"RAM is used for permanent storage"	RAM is volatile — temporary, not permanent
"Secondary storage is faster than primary memory"	Primary memory (RAM) is much faster
"ROM is used to store user data"	ROM stores boot instructions, not user data
"Removable storage and secondary storage are the same"	Removable storage is a subset of secondary storage
"Input devices output data"	Input devices enter data; output devices present data

Embedded System

An embedded system is a computer system that is built into (embedded within) a larger device to perform a specific, dedicated function. It is not a general-purpose computer.

Characteristic	Explanation
Dedicated function	Performs one specific task (or a limited set of tasks)
Embedded	Built into the larger device it controls
Limited resources	Often has limited memory, processing power, and storage
Real-time operation	Often must respond to events within strict time limits
Specialised hardware/software	Hardware and software are optimised for the specific task
Minimal user interface	May have no keyboard/mouse — often uses buttons, LEDs, or touchscreens

Examples of Embedded Systems

Device	Embedded System's Function
Washing machine	Controls wash cycles, water temperature, spin speed
Microwave oven	Controls cooking time, power level, turntable
Car engine management	Controls fuel injection, ignition timing, emissions
Digital watch	Displays time, sets alarms, measures stopwatch
Smart TV	Decodes digital signals, displays menus, connects to internet
Traffic light controller	Controls light sequences based on timers/sensors
Medical monitor	Monitors heart rate, blood pressure, oxygen levels
Printer	Controls paper feed, ink distribution, print heads

Benefits of Embedded Systems

Benefit	Explanation
Dedicated function	Optimised for one specific task, making them efficient and reliable
Low cost	Designed to do only one job — no unnecessary components = cheaper to manufacture
Small size	Can be miniaturised to fit into small devices
Low power consumption	Often designed to use minimal power (important for battery-operated devices)
High reliability	Fewer components and simpler software = fewer points of failure
Real-time response	Can respond to events immediately (e.g., airbag deployment)
Firmware updates	Can sometimes be updated to fix bugs or add features
Mass production	Once designed, can be produced in large quantities at low cost

Drawbacks of Embedded Systems

Drawback	Explanation
Limited functionality	Cannot be repurposed — only does what it was designed to do
Difficult to upgrade	Hardware is fixed; upgrades often require replacing the entire device
Limited resources	Limited memory, storage, and processing power compared to general-purpose computers
Specialised development	Requires specialised knowledge to develop hardware and software
Security concerns	Many embedded systems lack strong security; vulnerabilities can be hard to patch
Difficult to debug	Limited user interface makes debugging and error diagnosis challenging
Obsolescence	Technology moves fast; embedded systems can become outdated quickly
Programming complexity	Often require low-level programming and careful memory management

Embedded vs General-Purpose Computer

Feature	Embedded System	General-Purpose Computer
Purpose	Dedicated, specific task	Versatile, many tasks
User interface	Minimal (buttons, LEDs)	Rich (keyboard, mouse, screen)
Operating System	Often no OS or RTOS	Full OS (Windows, Linux, macOS)
Resources	Limited (low memory, small storage)	High (lots of RAM, large storage)
Cost	Low	Higher
Power consumption	Low	High
Upgradability	Difficult or impossible	Easy
Examples	Microwave, washing machine	Desktop PC, laptop, smartphone

Hardware

LASER PRINTER

Aspect	Description
Type	Output device (hard copy / printout)
Principal operation	Uses a laser beam and electrostatic charges to transfer toner (powdered ink) onto paper

Simple bullet-point process:

A laser beam is scanned across a rotating drum to create an electrostatic image
The drum is charged electrically; the laser removes charge where text/images should appear
Toner (fine black or coloured powder) is attracted to the charged areas
The drum rotates and transfers toner onto the paper
The paper passes through heated rollers (fuser unit) to melt/bond the toner permanently
Produces high-quality, fast, quiet printing

Key Cambridge points:

Electrostatic charge and laser create the image
Toner is used (not liquid ink)
Fuser unit bonds toner to paper using heat

3D PRINTER

Aspect	Description
Type	Output device (creates physical 3D objects)
Principal operation	Builds three-dimensional objects layer by layer from a digital design

Simple bullet-point process:

Reads a 3D digital model (from CAD software)
Heats and extrudes filament (plastic, resin, or metal) through a nozzle
Builds the object layer by layer from the bottom up
Each layer is deposited and hardens before the next layer is added
Creates solid, physical objects from digital designs

Key Cambridge points:

Additive manufacturing — builds up material rather than cutting away
Layer-by-layer construction
Used in prototyping, manufacturing, and medicine

MICROPHONE

Aspect	Description
Type	Input device (captures sound)
Principal operation	Converts sound waves (analogue) into electrical signals (digital)

Simple bullet-point process:

Sound waves cause a diaphragm (thin membrane) to vibrate
The vibrations are converted into electrical analogue signals
An Analogue-to-Digital Converter (ADC) converts the analogue signal into digital data
The digital data is sent to the computer for processing/storage

Key Cambridge points:

Sound waves (air pressure changes) → diaphragm vibration → electrical signal
ADC is essential for digital computers
Used for voice input, recording, video conferencing

SPEAKER

Aspect	Description
Type	Output device (produces sound)
Principal operation	Converts digital audio data into sound waves

Simple bullet-point process:

Computer sends digital audio data to the speaker
A Digital-to-Analogue Converter (DAC) converts the digital data into analogue electrical signals
The analogue signal causes a cone/diaphragm to vibrate
Vibrations create sound waves that travel through the air
User hears the sound

Key Cambridge points:

Digital → Analogue conversion via DAC
Electromagnetic coil and diaphragm create vibrations
Sound waves are produced for the user to hear

MAGNETIC HARD DISK DRIVE

Aspect	Description
Type	Secondary storage (non-volatile, magnetic)
Principal operation	Stores data magnetically on rotating platters coated with magnetic material

Simple bullet-point process:

Data is stored on rigid metal/glass platters coated with a magnetic material
Platters spin at high speed (e.g., 5400/7200 RPM)
Read/write head floats just above the platter surface
To write: head magnetises tiny areas (magnetic domains) to represent 1s and 0s
To read: head detects the magnetic orientation of the domains
Data is stored in tracks and sectors on the platters
Actuator arm moves the head across the platter to access different tracks

Key Cambridge points:

Magnetic storage (non-volatile)
Moving parts (platters spin, heads move)
Slower than solid-state due to mechanical movement
Large capacity and low cost per GB

SOLID STATE (FLASH) DRIVE

Aspect	Description
Type	Secondary storage (non-volatile, electronic)
Principal operation	Stores data electronically using floating-gate transistors (no moving parts)

Simple bullet-point process:

Data is stored in floating-gate transistors (cells)
Each cell traps electrons to represent data (charge = 1, no charge = 0)
To write: apply high voltage to trap electrons in the floating gate
To erase: apply voltage to release electrons (reset to 0)
To read: detect whether electrons are present (voltage threshold)
Cells are organised into blocks and pages
No moving parts → faster, quieter, more reliable than magnetic disks

Key Cambridge points:

Solid-state — no moving parts
Non-volatile — retains data without power
Faster than magnetic storage but more expensive per GB
Used in SSDs, USB drives, SD cards

OPTICAL DISC

Aspect	Description
Type	Secondary storage (removable, optical)
Principal operation	Reads/writes data using a laser beam on a reflective disc surface

Simple bullet-point process:

Disc has a spiral track of microscopic pits and lands on a reflective layer
Laser beam is shone onto the disc surface
To read: laser reflects differently off pits and lands → sensor detects changes
- Pits scatter light; lands reflect light back → interpreted as binary data
To write (recordable discs): laser burns marks into a dye layer
To rewrite (rewritable discs): laser changes crystalline state of a phase-change layer
Disc spins as the laser moves across its radius

Types:

Type	Capacity	Features
CD	700 MB	Read-only or write once
DVD	4.7 GB (single layer)	Higher capacity than CD
Blu-ray	25–100 GB	Uses blue laser (shorter wavelength = higher density)

Key Cambridge points:

Laser reads/writes data
Pits and lands (reflective differences)
Spiral track from centre to edge
Blue laser = higher density (Blu-ray)

TOUCHSCREEN

Aspect	Description
Type	Both input and output device (combined)
Principal operation	Detects touch on the screen surface, allowing user interaction

Types (Cambridge expects two):

Capacitive Touchscreen

Aspect	Description
Material	Glass screen with transparent conductive layer
Operation	Human finger is conductive → changes the electrostatic field at touch point
Advantage	More sensitive, supports multi-touch
Disadvantage	Won't work with gloved fingers or non-conductive stylus
Use	Smartphones, tablets, modern touchscreens

Resistive Touchscreen

Aspect	Description
Material	Two flexible layers separated by tiny gaps
Operation	Pressure causes layers to touch, changing the electrical resistance
Advantage	Works with any input (finger, stylus, gloved hand)
Disadvantage	Less sensitive, no multi-touch, can scratch
Use	Older devices, ATMs, medical equipment

Simple bullet-point process (general):

User touches the screen with finger or stylus
Sensors detect the position of the touch (X and Y coordinates)
The detected coordinates are sent to the processor
Software interprets the touch (e.g., as a click, drag, or gesture)
Screen also displays output (acting as an output device)

Key Cambridge points:

Capacitive: uses conductivity of human finger
Resistive: uses pressure to detect touch
Serves as both input and output device

VIRTUAL REALITY

Aspect	Description
Type	Both input and output device (combined)
Principal operation	Creates an immersive 3D environment by displaying stereoscopic images and tracking head/body movements

Simple bullet-point process:

Output: Displays separate images to each eye via small screens/lenses → creates 3D stereoscopic depth
Input: Uses sensors (gyroscopes, accelerometers, magnetometers) to track head movement
Input: May use external sensors/cameras for positional tracking (movement in room)
Input: Hand controllers track user's gestures/hand movements
Computer renders the virtual world in real-time based on where user is looking/moving
User perceives being immersed in a 3D virtual environment

Key Cambridge points:

Stereoscopic display (two screens = 3D perception)
Head tracking (gyroscopes/accelerometers) for rotation
Positional tracking for movement in 3D space
Low latency is essential (must respond quickly to head movements)
Used for gaming, simulation, training, and education

BUFFER

A buffer is a temporary storage area in memory (RAM) used to hold data while it is being transferred between two devices or processes that operate at different speeds.
Analogy: A buffer is like a queue at a supermarket checkout. Customers (data) arrive faster than the cashier (slow device) can serve them. The queue (buffer) holds customers until the cashier is ready.

Printer Buffer

Aspect	Description
Problem	Printer is slow; CPU is fast
Solution	Print job is sent to a printer buffer
Operation	CPU sends entire document to buffer quickly; printer reads from buffer slowly
Benefit	CPU can continue other work while printer prints

Video Streaming Buffer

Aspect	Description
Problem	Network speed varies; video must play smoothly
Solution	Video data is pre-loaded into a buffer
Operation	Buffer stores several seconds of video before playback begins
Benefit	Prevents buffering/stuttering if network speed drops

Benefits of a buffer

Speed matching	Allows fast and slow devices to work together efficiently
No data loss	Prevents data loss when fast device outpaces slow device
CPU efficiency	CPU can continue working while I/O device catches up
Smooth playback	Prevents buffering/stuttering in streaming media
Batch processing	Allows data to be collected and processed in batches

Drawbacks of a buffer

Drawback	Explanation
Memory usage	Requires additional RAM for temporary storage
Latency	Adds slight delay (data must be stored before processing)
Buffer overflow	If buffer fills up, data may be lost
Buffer underrun	If buffer empties, slow device may stall

ROM AND RAM

Feature	RAM	ROM
Volatility	Volatile — data lost when power is removed	Non-volatile — data retained when power is removed
Read/Write	Read and Write — data can be read from and written to	Read Only — data cannot normally be modified
Purpose	Stores active programs and data currently in use	Stores boot-up instructions (BIOS/UEFI)
Speed	Faster than ROM	Slower than RAM
Capacity	Larger (GBs: 4GB – 128GB)	Smaller (MBs: 2MB – 64MB)
Cost	More expensive per GB	Cheaper per GB
Contents	Changes constantly as programs run	Fixed at time of manufacture
Location	Main memory (system memory)	Main memory (usually on motherboard)
Usage	OS, applications, user data	System startup, firmware, bootstrap loader
Type	Dynamic (DRAM) or Static (SRAM)	Mask ROM, PROM, EPROM, EEPROM

Types of RAM:

Type	Description
DRAM (Dynamic RAM)	Needs to be refreshed thousands of times per second; slower but cheaper; used for main memory Consists of transistors and capacitors Higher memory Consumes more power than SRAM
SRAM (Static RAM)	Does not need refreshing; faster but more expensive; used for cache memory make use of flip-flops. Can us