Secondary storage: magnetic, optical and solid state Cambridge IGCSE Computer Science revision
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In plain words
RAM forgets everything when the power goes off, so a computer needs somewhere permanent to keep its files and programs. That is secondary storage. It comes in three types, named after the physics each one uses to store a bit.
6 things to know
- Secondary storage is not directly accessed by the CPU. It is non-volatile, and it is needed for more permanent storage of data.
- Magnetic storage, such as a hard disk drive (HDD): spinning platters are divided into tracks and sectors. Data is read and written by electromagnets in a read/write head, which magnetise tiny areas of the surface.
- An HDD stores a lot for a low cost, but it has moving parts, so it is slower, noisier and can be damaged if it is dropped.
- Optical storage, such as CD, DVD and Blu-ray: a laser reads a pattern of pits and lands on the surface of the disc. The two reflect the light differently.
- Solid-state storage (flash memory), such as a solid-state drive (SSD), an SD card and a USB drive: it uses NAND or NOR technology. Transistors act as control gates and floating gates, and electrons trapped in the floating gate store the data.
- Solid-state storage has no moving parts, so it is fast, quiet, robust and uses little power. It costs more for each gigabyte.
Worked example
A student needs storage for a laptop that will be carried to school every day. Which type is most suitable?
- The laptop will be moved around and may be knocked.
- A hard disk drive has moving parts that can be damaged by a knock.
- A solid-state drive has no moving parts, so it is more robust. It is also lighter, uses less power (so the battery lasts longer) and loads files faster.
- A solid-state drive is the most suitable.
Tips and tricks
- Three types, three key words: magnetic uses electromagnets, optical uses lasers, solid state uses transistors.
- "Tracks and sectors" go with magnetic. "Pits and lands" go with optical. "Control gates and floating gates" go with solid state.
It lands in your notebook with its questions as flashcards.
Secondary storage: magnetic, optical and solid state: 6 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
Which type of storage uses platters divided into tracks and sectors?
A hard disk drive is magnetic.
Which type of storage is read using a laser?
CDs, DVDs and Blu-ray discs.
Which of these is solid-state storage?
So are SSDs and USB drives.
Why is a solid-state drive more robust than a hard disk drive?
There is no spinning platter or moving head to damage.
What do pits and lands do on an optical disc?
The difference in reflection is read as binary.
Why does a computer need secondary storage?
RAM loses everything without power.
Quiz
6 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
2 questions, 5 marks. Write your answers on paper, then check them.
Secondary storage: magnetic, optical and solid state
Cambridge IGCSE Computer Science 0478 · 5 marks · papermunch.org
Name ______________________________ Date ______________
Describe how data is stored on and read from an optical disc.[3]
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A laser burns a pattern of pits into the surface, leaving flat lands between them. To read the disc, a laser is shone at it. Pits and lands reflect the light differently, and this is read as 1s and 0s.
Give two advantages of a solid-state drive compared with a hard disk drive.[2]
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It has no moving parts, so it is more robust. It reads and writes data faster. (Also: it is quieter and uses less power.)
Answers: Secondary storage: magnetic, optical and solid state
- 1. A laser burns a pattern of pits into the surface, leaving flat lands between them. To read the disc, a laser is shone at it. Pits and lands reflect the light differently, and this is read as 1s and 0s.
- 2. It has no moving parts, so it is more robust. It reads and writes data faster. (Also: it is quieter and uses less power.)