Types of secondary storage
There are three types of secondary storage:
- Optical storage
- Magnetic storage
- Solid state storage
Optical storage
Optical storage includes CD, DVD and Blu-Ray disks.
It uses high powered lasers to burn information onto the disks and weak lasers to read that information.
Optical storage is used less and less these days but has historically been useful for cheap and easy distribution of programs and data. Nowdays this is more likely to be done via online download but optical disks can still be bought quite cheaply.
Magnetic storage
Magnetic storage is used in hard disk drives and magnetic tape.
Data is stored on disk shaped platters for hard disks or tape by magnetising sections with north or south polarity. This can be read back as 1 or 0.
A hard disk drive has moving parts making it slower at retrieving data than solid state storage but it is cheaper per byte than solid state storage so is often used as the main storage for computers and magnetic tape is
often used for backing up networks.
Hard drives can be internal or external. They are less durable than solid state drives but advances in small portable hard drives mean they are now often carried around in laptop bags and are smaller, lighter and less prone to damage.
Solid state storage
Solid state storage refers to SSD style hard drives and USB sticks.
Solid state storage uses electrons that can be trapped by a semi-impermeable barrier. They can then be read back as trapped or not trapped.
They have no moving parts making them efficient at transferring data and highly durable
Solid state storage is used in devices that need to be portable like phones and tablets and is increasingly used as secondary storage in computers due to its speed advantages and decreasing costs per GB.
Comparing secondary storage methods
You need to be able to evaluate different secondary storage devices and their usefulness in given scenarios. The criteria you need to judge them on are capacity, speed, portability, durability, reliability.
| Characteristic |
Optical |
Magnetic |
Solid state |
| Capacity |
CD 650-700 MB; DVD 4.7 GB; Blu-ray 25 GB |
From 500 MB up to 20 TB |
From 64 MB up to 10 TB |
| Speed |
Slow read speeds, very slow write speeds |
Medium speed read and write |
Fast read and write |
| Portability |
Easily transported as they are lightweight and can be protected in a case |
Less portable than the others but improvements make this less of a concern than it used to be |
Smaller and lighter than other methods so very portable |
| Durability |
Can be scratched when out of their case |
Should not really be moved when in use and subject to interference from electricity and magnets |
Very durable due to having no moving parts |
| Reliability |
They have a lifespan of about 5-10 years and can be damaged by sunlight and scratches |
Highly reliable and can be written read and rewritten virtually endlessly |
Very reliable but has a maximum number of write cycles but this number is quite high |
| Cost |
Disks remain cheap to buy but many newer computers have no disk drive |
The cheapest overall storage per GB |
Traditionally very expensive, and still more expensive than the others, but dropping in price rapidly as it grows in popularity and more is produced |
Applying your knowledge in context
This means being able to use the relative advantages and disadvantages above to justify a suitable choice of storage device. A key thing to remember with this type of uestion is that you need to say both what its advantage
is and why that is useful in the scenario e.g. A question about the storage needed by a DJ that has thousands of songs they need to take to gigs with them might be answered by suggesting either solid state or magnetic. If you
chose solid state you might go on to talk about it being durable and therefore suitable to carry around or more portable because it is small and lightweight making it easy to carry anywhere he goes or fast to load new songs on
to.