1.2 The main components of computer systems
Cambridge IGCSE ICT 0417 · Topic 1: Types and components of computer systems · Paper 1
2.1 Input devices
Cambridge IGCSE ICT 0417 · Topic 2: Input and output devices · Paper 1
3.4 Solid-state storage and backing up
Cambridge IGCSE ICT 0417 · Topic 3: Storage devices and media · Paper 1
Say each word, then read what it means. Every one is in the glossary too.
Read it here, or open the study page below to go one step at a time with things to try.
| Paper | Type | Time | Marks | Share of the grade |
|---|---|---|---|---|
| Paper 1 Theory | Written | 1 hour 30 minutes | 80 | 40% |
| Paper 2 Document Production, Databases and Presentations | Practical | 2 hours 15 minutes | 70 | 30% |
| Paper 3 Spreadsheets and Website Authoring | Practical | 2 hours 15 minutes | 70 | 30% |
Paper 1 is 80 marks in 90 minutes. That is just over a minute a mark, with about 10 minutes to check.
The glossary words are the mark-scheme words. Use them.
| Command word | What it wants | One-mark example |
|---|---|---|
| Describe | A feature, plus how it works | A chip and PIN reader reads the chip on the card, and the customer types a PIN to confirm. |
| Explain | A point, plus why | An SSD has no moving parts, so it is less likely to be damaged if the laptop is dropped. |
| Compare | Both sides in the same point | A laser printer is faster for large print runs, whereas an inkjet printer is slower. |
In 'explain', a point with no 'because' or 'so' often earns nothing.
Many questions ask for an advantage and a disadvantage. Always give them as a matched pair.
Always link them to the situation in the question.
Question: give one advantage and one disadvantage of online cinema booking for the customer. Advantage: they can book at any time, from home, without queuing at the cinema. Disadvantage: they need internet access, and their card details could be stolen.
'It is faster' or 'it is cheaper' alone rarely earns a mark. Say what is faster, and faster than what.
The central processing unit (CPU) carries out the instructions in programs. It is also called the processor.
It fetches an instruction from memory, works out what it means, then does it. This happens billions of times a second.
It contains the control unit (manages the order of instructions) and the arithmetic logic unit (ALU) (does calculations and comparisons).
Everything a computer does, from opening a file to adding up a column, is instructions being processed by the CPU.
RAM (random access memory) holds the data and programs that are in use now. It is volatile: the contents are lost when the power is off. It can be read from and written to.
ROM (read-only memory) holds instructions that must never be lost, such as the start-up instructions (BIOS). It is non-volatile: it keeps its contents with no power. It can be read but not normally changed.
RAM is usually much bigger than ROM. A laptop might have 16 GB of RAM but only a few MB of ROM.
| RAM | ROM | |
|---|---|---|
| Volatile? | Yes, lost when power off | No, kept when power off |
| Read / write | Read and write | Read only |
| Holds | Programs and data in use now | Start-up (boot) instructions, BIOS |
| Size | Large (e.g. 8–32 GB) | Small (e.g. a few MB) |
| Changes while working? | Yes, all the time | No |
Do not write "RAM is temporary storage" alone. Say why: it is volatile, so data is lost when the power is turned off.
An input device sends data or instructions into the computer. Examples: keyboard, mouse, microphone, scanner.
An output device shows or does the result from the computer. Examples: monitor, printer, speaker.
A touch screen is both. Touching it is input. The picture it shows is output.
Internal memory is RAM and ROM. The CPU can reach it directly and fast.
Backing storage keeps data and programs long-term, even with no power. Examples: hard disk drive, solid-state drive, USB pen drive.
Programs live on backing storage. When you open one, it is copied into RAM, because the CPU can only work with what is in memory.
| Internal memory (RAM/ROM) | Backing storage | |
|---|---|---|
| Access by CPU | Direct | Not direct; copied into RAM first |
| Speed | Very fast | Slower |
| Capacity | Smaller | Much larger (e.g. 1 TB) |
| Cost per GB | Higher | Lower |
| Volatile? | RAM yes, ROM no | No |
An input device lets data or instructions go into a computer.
Some are manual: a person operates them, like a keyboard. Others capture data automatically, like a sensor.
When you answer an exam question, name the device, say what it is used for, then give a reason linked to the situation.
A keyboard is used to type text and commands. Most use the QWERTY layout.
A concept keyboard has flat keys with pictures or words. Fast-food tills use them.
A numeric keypad has only numbers and a few keys. It is on ATMs, chip and PIN terminals, phones and the side of large keyboards.
| Device | Use | Advantage | Disadvantage |
|---|---|---|---|
| Keyboard | Typing documents, emails, data into forms | Fast, accurate entry of text for a trained typist; familiar to most users | Slow for people who cannot type; long use can cause RSI; takes up desk space |
| Numeric keypad | Entering PINs at an ATM, prices at a till, phone numbers | Faster than a full keyboard for numbers; small, so fits on a card terminal | Keys are small and can be hard to press; PIN can be seen by shoulder surfing |
A pointing device moves a pointer (cursor) on a screen and selects things.
A mouse is moved on a desk. A touchpad is a flat pad on a laptop: you move a finger on it. A trackerball is like an upside-down mouse: you roll the ball and the device stays still.
| Device | Use | Advantage | Disadvantage |
|---|---|---|---|
| Mouse | Selecting icons and menus in a GUI; drawing | Faster to select options than using keyboard shortcuts; easy to use | Needs a flat surface; can cause RSI with long use |
| Touchpad | Pointing on a laptop | Built in, so no extra device to carry; works where there is no desk | Harder to control precisely than a mouse, e.g. for drawing |
| Trackerball | People with limited hand movement; control rooms; some medical equipment | Does not move, so needs less space and less wrist movement; easier for some disabilities | Not as fast as a mouse for most users; costs more |
A remote control sends infrared or radio signals to a TV, projector or air conditioner from a distance.
A joystick controls movement in games and flight simulators. A driving wheel controls steering in driving games and car simulators.
| Device | Use | Advantage | Disadvantage |
|---|---|---|---|
| Remote control | Changing TV channel; controlling a projector or a multimedia system | Can be used from a distance, so the user does not need to move | Infrared needs a clear line of sight; small buttons hard for some people; easy to lose |
| Joystick | Games; flight simulators; controlling robot arms | Easier to control movement in any direction than with keys; feels realistic | Harder to use for selecting menus or typing |
| Driving wheel | Driving games and training simulators | More realistic than a keyboard, so training is more useful | Expensive; takes up space; only useful for one kind of task |
A touch screen is a screen you touch to select options. It is used on phones, tablets, ATMs, information kiosks and self-service tills.
A light pen is a pen with a light sensor. You point it at a screen to draw or select. It is rare now and is used in some design and medical work.
| Device | Use | Advantage | Disadvantage |
|---|---|---|---|
| Touch screen | Phones, ATMs, kiosks, self-service checkouts | Fast and intuitive, no training needed; no keyboard or mouse, so saves space | Screen gets dirty and scratched; limited options per screen; hard for some disabilities |
| Light pen | Drawing directly on screen; selecting on medical or design screens | More precise than a finger; no desk space needed | Can be tiring to hold up against a screen; not suitable for all screen types |
A scanner turns a paper document or photo into a digital image.
A digital camera takes photos and videos and stores them on a memory card.
A microphone turns sound into an electrical signal. Uses: video calls, voice recognition, recording.
| Device | Use | Advantage | Disadvantage |
|---|---|---|---|
| Scanner | Digitising old photos and documents; with OCR, turning print into editable text | Faster than retyping or redrawing; makes a digital backup of paper | Quality depends on the original; large image files |
| Digital camera | Photos for websites, ID cards, reports | Images can be checked at once and deleted; easy to transfer to a computer | High-quality images use a lot of storage; good cameras are expensive |
| Microphone | Voice recognition, video calls, voice notes | Faster than typing for many users; hands-free | Background noise affects quality; voice recognition makes errors |
A sensor measures a physical quantity, such as temperature, and sends the reading to a computer. The data is usually analogue, so an ADC converts it.
Sensors take readings automatically and continuously, day and night. A person does not need to be there.
| Sensor | Measures | Example use |
|---|---|---|
| Temperature | How hot or cold | Central heating, greenhouses, ovens |
| Light | Light level | Street lights turning on at dusk; phone screen brightness |
| Pressure | Force or weight | Burglar alarm mats; car airbags; checking tyre pressure |
| Moisture / humidity | Water in soil or air | Watering plants in a greenhouse; museums |
| Infrared / motion | Movement or heat from a body | Security lights; automatic doors |
| Sound (acoustic) | Noise level | Burglar alarms detecting breaking glass |
| pH | Acidity | Fish tanks; checking river pollution |
| Gas (e.g. CO2, oxygen) | Gas levels | Greenhouses; carbon monoxide alarms |
Advantage: readings are more accurate and more frequent than a person could take, and work in dangerous places. Disadvantage: a faulty sensor gives wrong data, and sensors cost money to install and maintain.
A sensor does not "control" anything. It only measures. The microprocessor decides and an actuator acts.
Solid-state storage stores data in electronic chips called flash memory. Tiny transistors trap electric charge to hold 1s and 0s.
It has no moving parts. That is why it is fast, quiet, light and tough.
It is non-volatile: the charge stays trapped when the power is off.
A solid-state drive (SSD) replaces a hard disk inside a laptop or desktop. Most new laptops and all phones use solid-state storage.
| SSD | HDD | |
|---|---|---|
| Moving parts | None | Spinning platters and moving head |
| Speed | Faster: computer starts and opens files more quickly | Slower |
| Durability | More robust: survives being dropped | Can be damaged if dropped while running |
| Power and heat | Uses less power, so laptop battery lasts longer | Uses more power, produces more heat |
| Noise and weight | Silent, lighter, thinner | Some noise, heavier |
| Cost per GB | Higher | Lower |
| Lifespan | Each part can be rewritten only a limited number of times | Mechanical wear over time |
Always compare: "An SSD is faster than an HDD because it has no moving parts, so there is no wait for the disk to spin."
A pen drive (USB flash drive) is a small solid-state device that plugs into a USB port. Used to carry files between school and home.
A memory card is a thin solid-state card used in cameras, phones, drones and games consoles.
SD (Secure Digital) cards are the most common, including microSD in phones. xD cards were used in older digital cameras. CFast cards are very fast and are used in professional video cameras.
| Device | Advantage | Disadvantage |
|---|---|---|
| Pen drive | Very portable and robust; works in almost any computer by USB | Easy to lose or steal, so data should be encrypted; can carry viruses between computers |
| Memory card (SD, xD, CFast) | Tiny and light, so ideal for cameras and phones; no moving parts | Easy to lose; small cards are easy to damage; some devices accept only one card type |
Choose storage by asking: How much data? How fast? How portable? How tough? How much money? Will it be changed?
Try the picker. Read each job, choose magnetic, optical or solid-state, and read why.
| Job | Good choice | Why |
|---|---|---|
| Selling a film in shops | Blu-ray ROM | Cheap to make, cannot be changed |
| Archiving a bank's records every night | Magnetic tape | Huge capacity, lowest cost per GB, serial order is fine for a backup |
| Storage in a smartphone | Solid-state (flash) | Small, light, low power, no moving parts |
| A school file server | Fixed HDD (or SSD) | Large capacity at low cost, direct access |
| Professional video camera | CFast or SD card | Fast enough to record high-quality video, tiny |
There is something to try for this step in the IGCSE library.
A backup is a copy of data kept separately, so it can be restored if the original is lost.
Data can be lost through hardware failure, accidental deletion, theft, fire or flood, or malware such as ransomware.
Good practice: back up regularly, keep at least one copy in a different place (off-site or in the cloud), and test that the backup can be restored.
A backup kept next to the computer is lost in the same fire or theft. Distance is the point.
A backup is not the same as archiving. A backup is a copy for recovery. An archive moves old data off the main system to keep it long-term.
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Topic 1 · Year 7A computer takes information in, follows instructions to change it, and gives a result out. It does all of this with billions of tiny on/off switches.
Topic 8 · Year 8The CPU does the work, RAM holds what it's using now, and storage keeps everything long-term. The CPU repeats one loop: fetch, decode, execute.
One question at a time. The reason shows after each answer.