3.2 Magnetic storage
Cambridge IGCSE ICT 0417 · Topic 3: Storage devices and media · Paper 1
3.3 Optical storage
Cambridge IGCSE ICT 0417 · Topic 3: Storage devices and media · 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.
Data is stored as tiny magnetised areas on a surface. One direction of magnetism means 1, the other means 0.
A read/write head changes the magnetism to write data and senses it to read data.
In a hard disk drive (HDD) the disks (platters) spin very fast and the head moves across them on an arm. These are moving parts.
Moving parts explain the main disadvantages: HDDs are slower than solid-state, use more power, make noise and can be damaged if dropped.
A fixed HDD is built into a computer or server. It stores the operating system, programs and user files.
A portable HDD is in its own case and plugs in by USB. It is used for backups and to move large files.
HDDs use direct access: the head can go straight to any part of the disk, so files are found quickly.
| Advantages | Disadvantages |
|---|---|
| Large capacity (several TB) at low cost per GB, so good for servers and backups | Moving parts can break, especially if a portable drive is dropped |
| Fast direct access to any file, faster than tape | Slower to read and write than an SSD |
| Data can be overwritten many times | Uses more power and makes more noise and heat than an SSD |
| Portable HDD: easy to unplug and store away from the computer | Can be damaged by strong magnets |
Magnetic tape is a long plastic strip with a magnetic coating, wound on a reel inside a cartridge.
It uses serial access: data is read in order from the start, like fast-forwarding a song. Finding one file is slow.
Uses: large organisations back up and archive huge amounts of data, such as a bank's records or a hospital's old scans.
| Advantages | Disadvantages |
|---|---|
| Very large capacity (many TB per cartridge) and the lowest cost per GB | Serial access, so finding one file is very slow |
| Ideal for backups, because a backup copies everything in order anyway | Needs a special tape drive |
| Tapes are robust and last many years in storage | Not suitable for files that are used often |
Tape is not "out of date". It is still the cheapest way to archive very large amounts of data.
Data is stored as tiny pits and flat areas (lands) on a shiny disc, along one long spiral track.
A laser shines on the disc. Pits and lands reflect light differently, which gives the 1s and 0s.
A shorter laser wavelength makes a smaller spot, so pits can be smaller and closer together. That is why Blu-ray holds more.
All three are the same size. The difference is how tightly the data is packed.
Dual layer discs have two layers of data, so they hold almost twice as much.
| CD | DVD | Blu-ray | |
|---|---|---|---|
| Typical capacity | 700 MB | 4.7 GB (8.5 GB dual layer) | 25 GB (50 GB dual layer) |
| Laser | Red, longest wavelength | Red, shorter wavelength | Blue-violet, shortest wavelength |
| Typical use | Music, small software | Films (standard definition), software | High-definition and 4K films, games |
ROM (read-only memory): data is written at the factory and cannot be changed. Used for films and software sold in shops, so customers cannot delete or change it.
R (recordable): you can write to it once, then it becomes read only. Used to keep a permanent copy, such as exam records or wedding videos.
RW (rewritable): you can write, erase and rewrite many times. Used for temporary backups or moving files.
| Type | Write? | Advantage | Disadvantage |
|---|---|---|---|
| ROM | No, read only | Data cannot be deleted or changed by accident | Cannot be updated |
| R | Once | Permanent copy that cannot be altered; cheap | A mistake wastes the disc; cannot add or update later |
| RW | Many times | Can be reused, so less waste | Data can be overwritten by mistake; more expensive than R |
Optical discs are used less now, because people stream films and download software. They are still used for films, games and long-term archives.
| Advantages | Disadvantages |
|---|---|
| Cheap to make, so good for selling films and software | Small capacity compared with HDDs and SSDs |
| Light and easy to post | Easily scratched, which can make data unreadable |
| ROM discs cannot be changed, so content is safe | Slower to access than HDDs and SSDs |
| Not affected by magnets | Many new laptops no longer have an optical drive |
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.
Open the study page and go one step at a time.
Step by step, with exam questions and a quiz.
ICT topic 2Step by step, with exam questions and a quiz.
ICT topic 3Step by step, with exam questions and a quiz.
ICT topic 11Step by step, with exam questions and a quiz.
ICT topic 17Step by step, with exam questions and a quiz.
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.
Topic 2 · Year 7A bit is one switch: 0 or 1. A byte is 8 bits. Every file is measured by counting these.
Symbols first, then the words, then the equation. Change the numbers to try your own.
One question at a time. The reason shows after each answer.