- Key Topics
- Primary Storage
- Secondary Storage
- Magnetic Storage
- Optical Storage
- Solid State Storage
Key topics for OCR GCSE Computer Science: Secondary Storage Devices
For the OCR Exam you need to know:
Why do we need secondary storage?
How to calculate data capacity?
What are the 3 common types of storage devices and how do they work?
What are the advantages and disadvantages of different storage devices when considering:
Primary storage is the CPU’s memory. Due to it’s volatile nature it is very very fast.
It consists of:
Whilst primary storage is fast, it has 2 problems:
- It is quite small ( RAM 8GB, Cache 512Kb)
- It is volatile – when you turn off the computer, that data goes!
Because of this we need secondary storage!
Secondary storage is:
- Non – volatile – the data remains even when the power is gone.
- Slower than primary storage
- Much larger in capacity
Examples of secondary storage:
- CD Rom Drives
- ROM Chips
- USB Sticks
- SSD Drives
- Magnetic tape drives
Magnetic Storage Devices
These are the oldest of the commonly used storage devices, but are still the most widely used.
- Magnetic Hard Drives are used to store data and programs on desktops and laptops
- Magnetic tape drives are usually used for large server / systems backups.
- Cheap Storage per MB (especially tape drives!)
- Relatively quick read / write speeds.
- Easily broken if dropped
- Slow read /write compared to new SSD drives.
How they work
Optical Storage Devices
Types of optical storage devices:
- CD Drives
- DVD Drives
- BluRay Drives
Optical storage devices offer cheap and portable high capacity secondary storage. Far more portable than an internal harddrive, which makes them good for small / medium size backups and great for sending through the post.
How they work
Optical storage devices work by firing a laser at the surface of a spinning disk. The disc is covered in a pattern of pits in the CD surface. As the laser hits the pits it is reflected and the pattern of pits it detected by a laser detector.
Solid State Storage Devices
Solid state storage devices work by storing data in flash chips electronically.
- Very fast read / write speeds.
- Shock resistant as there are no moving parts to break if knocked
- More expensive per GB of storage
- Limited life span, as each flash cell can only be written to a limited number of times.