Secondary Storage I
P03d
- Explain why secondary storage is needed.
- Describe how data is stored on magnetic, optical and solid-state media.
General purpose devices
P03d
The computing devices you use most of the time are ‘general purpose’ computers.
Desktops, laptops, smartphones, and tablets can be used for a huge variety of purposes. New software can be downloaded and installed to give additional functionality.
The reason computers exist as we know them is because of the stored program concept, conceived in the 1940s by Von Neumann and Alan Turing.
Remember that in the time before devices were able to store programs, they needed to be rebuilt or rewired in order to perform a different task
Secondary storage
P03d
In everyday computer use, you need a way to write data and to store data when your computer is switched off. You also need a way to retrieve data the next time you switch your computer back on.
RAM allows you to write data and store it … but this data is lost when your computer is switched off (because RAM is volatile memory).
Therefore, you need some way of reading and editing data AND storing the data when the computer has no power.
Practice I
P03d
Explain why secondary storage is necessary.
A computing device that can have different application programs loaded into it to provide different or enhanced functionality. For example, a smartphone can also be used as a calculator and a camera.
Define the term ‘general purpose device’.
RAM is volatile. It loses its contents when the power is switched off. Secondary storage provides non-volatile storage that can be used to write and rewrite data, so that it does not vanish when the power is turned off.
Storage technologies
P03d
There are three main types of storage technology that computers use:
- magnetic
- optical
- solid state
There is a difference between a storage device and the medium that it uses to store information.
- A DVD drive reads from and writes data to an optical disk medium.
- A hard disk reads from and writes data to a magnetic platter medium.
- A USB drive reads from and writes data to a solid-state/flash medium.
Magnetic
P03d
Magnetic media are coated with a substance that can be magnetised.
Magnetic storage technology works by magnetising parts of this substance as north and south poles to represent binary 1s and 0s.
Examples:
- hard disk drive
- tape drive
Optical
P03d
Optical media consist of a platter with a flat reflective surface.
Optical storage technology works by using a laser to burn ‘pits’ into the flat surface. The reflective areas between pits are known as ‘lands’.
Examples:
- DVD
- CD
A laser is directed onto the medium’s surface. When it hits a ‘land’ the beam reflects (this is read as a 1) but when it hits a ‘pit’, the beam does not reflect (this is read as a 0).
Solid state
P03d
Solid-state media consist of silicon chips that feature a special kind of transistor called NAND flash. This type of media is called ‘solid state’ because it has no moving parts.
Solid-state technology works by using a large electric current to force electrons through a barrier, trapping them in positions called ‘pools’.
Examples:
- SSD cards
- USB flash drive.
- The flash of the electric current used to achieve this gives us the name for this type of memory.
A full pool represents 0 and an empty pool represents 1.
Recap
P03d
Identify the type of storage:
Practice II
P03d
Watch the video and complete the table.
| Storage type and description | Advantages | Disadvantages |
|---|---|---|
| Optical | ||
| Magnetic | ||
| Solid state |
Practice II
P03d
Watch the video and complete the table.
Cheap to produce
Thin and lightweight
Portable
| Storage type and description | Advantages | Disadvantages |
|---|---|---|
| Optical |
||
| Magnetic |
||
| Solid state |
Slow to access
Low capacity
Prone to scratches
High capacity
Quick to access, providing the disk is defragmented periodically.
Has moving parts that will eventually fail.
Quick to access
No moving parts so very reliable
Low power requirements
Quiet
No need to defragment
Expensive compared to other types of storage.
Has a limited number of read-write cycles.
Review
P03d
Explain why secondary storage is needed.
- RAM is volatile which means that its content is lost when its power is switched off.
Describe how data is stored on magnetic, optical and solid-state media.
- Magnetic uses the polarisation of particles on a disk to represents 1s and 0s.
- Optical uses a laser and the pits and lands on the surface of a disk to represent 1s and 0s.
- Solid state uses electrons forced into pools to represent 1s and 0s.