Year 10 · ICT · Autumn 1
Computer systems, devices and storage; document production · Lesson 4 of 5
Storage devices and media
Theory3.2 Magnetic storage3.3 Optical storage3.4 Solid-state storage and backing up
Year 10 · ICT · Computer systems, devices and storage; document production · Lesson 4 of 5
You will learn to
- Describe how magnetic, optical and solid-state storage store data.
- Compare storage media for capacity, speed, cost and portability.
- Choose a suitable storage device for a given use and justify it.
- Explain why backups are needed and choose suitable backup media.
Year 10 · ICT · Computer systems, devices and storage; document production · Lesson 4 of 5
Success criteria
You have got it when you can say:
- I can say how each type of storage stores a bit.
- I can put CD, DVD and Blu-ray in order of capacity.
- I can choose storage for a school backup, a camera and a film, with a reason.
Year 10 · ICT · Computer systems, devices and storage; document production · Lesson 4 of 5
Retrieval starter
Questions from before. Write your answers, then show them.
- Last lesson
Which is application software?
A A device driverB The operating systemC A spreadsheet
C. A spreadsheet
- Earlier this unit
RAM is…
A The hard diskB Permanent storageC Volatile working memory
C. Volatile working memory
- Last lesson
A phablet is…
A A printerB Between a phone and a tablet in sizeC A server
B. Between a phone and a tablet in size
Year 10 · ICT · Computer systems, devices and storage; document production · Lesson 4 of 5
Key words (1 of 4)
- Storage medium
- The thing data is stored on, such as a disc or a chip.
- Storage device
- The hardware that reads and writes the storage medium.
- Backing storage
- Non-volatile storage that keeps data long-term.
- Capacity
- How much data a storage device can hold.
Year 10 · ICT · Computer systems, devices and storage; document production · Lesson 4 of 5
Key words (2 of 4)
- Magnetic storage
- Storing data as magnetised areas on a disk or tape.
- Optical storage
- Storing data as pits and lands on a disc, read by a laser.
- Solid-state storage
- Storing data in flash memory chips with no moving parts.
- Direct access
- Going straight to any piece of data, as on a disk.
Year 10 · ICT · Computer systems, devices and storage; document production · Lesson 4 of 5
Key words (3 of 4)
- Serial access
- Reading data in order from the start, as on a tape.
- R (recordable)
- An optical disc that can be written once.
- RW (rewritable)
- An optical disc that can be written and erased many times.
- ROM disc
- An optical disc written at the factory that cannot be changed.
Year 10 · ICT · Computer systems, devices and storage; document production · Lesson 4 of 5
Key words (4 of 4)
- Dual layer
- A disc with two data layers, so nearly double the capacity.
- Backup
- A copy of data kept separately so it can be restored if lost.
- Flash memory
- Non-volatile memory chips that store data as trapped electric charge.
3.2 Magnetic storage · The explanation · step 1 of 12 · part 1 of 2
How magnetic storage works
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.
3.2 Magnetic storage · The explanation · step 1 of 12 · part 2 of 2
How magnetic storage works (continued)
Moving parts explain the main disadvantages: HDDs are slower than solid-state, use more power, make noise and can be damaged if dropped.
3.2 Magnetic storage · The explanation · step 2 of 12 · part 1 of 2
Fixed and portable hard disk drives
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.
3.2 Magnetic storage · The explanation · step 2 of 12 · part 2 of 2
Fixed and portable hard disk drives (continued)
| 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 |
3.2 Magnetic storage · The explanation · step 3 of 12 · part 1 of 2
Magnetic tape
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.
3.2 Magnetic storage · The explanation · step 3 of 12 · part 2 of 2
Magnetic tape (continued)
| 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.
3.3 Optical storage · The explanation · step 4 of 12
How optical storage works
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.
3.3 Optical storage · The explanation · step 5 of 12 · part 1 of 2
CD, DVD and Blu-ray
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 |
3.3 Optical storage · The explanation · step 5 of 12 · part 2 of 2
CD, DVD and Blu-ray (continued)
3.3 Optical storage · The explanation · step 6 of 12 · part 1 of 2
R, RW and ROM
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.
3.3 Optical storage · The explanation · step 6 of 12 · part 2 of 2
R, RW and ROM (continued)
| 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 |
3.3 Optical storage · The explanation · step 7 of 12
Optical media: pros and cons
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 |
The explanation · 5 more steps
More on the lesson page
The lesson page has the rest of the explanation, step by step:
- How solid-state storage works
- SSD compared with HDD
- Pen drives and memory cards
- Pick the right storage
- Backing up
Year 10 · ICT · Computer systems, devices and storage; document production · Lesson 4 of 5
The maths: Changing units
Symbols first, then the words, then the equation. Change the numbers.
Year 10 · ICT · Computer systems, devices and storage; document production · Lesson 4 of 5
Quick quiz · 1 of 3
Exporting means…
- A Saving in a format another program can open
- B Printing
- C Deleting
A. Saving in a format another program can open
Importing is bringing a file in.
Year 10 · ICT · Computer systems, devices and storage; document production · Lesson 4 of 5
Quick quiz · 2 of 3
In mail merge, the master document holds…
- A The list of names
- B The envelope
- C The letter with the merge fields
C. The letter with the merge fields
The data source holds the names.
Year 10 · ICT · Computer systems, devices and storage; document production · Lesson 4 of 5
Quick quiz · 3 of 3
The data source is…
- A The list of recipients
- B The printer
- C The letter
A. The list of recipients
A spreadsheet or database table.
Year 10 · ICT · Computer systems, devices and storage; document production · Lesson 4 of 5
Exit ticket
Answer on paper before you go. Then check.
Selecting Year = 8 before merging…
A Sends letters only to Year 8B Changes the letter textC Prints everything twice
A. Sends letters only to Year 8 Selection criteria filter the recipients.
A merge field looks like…
A =SUM(A1)B «FirstName»C <p>
B. «FirstName» Show the field codes in your evidence.