1. Chapter 3: Storage devices and media Revision
Candidates should be able to: 1
Describe common backing storage media (including magnetic tapes, hard discs, all forms of CD and DVD, memory sticks, flash memory) and their associated devices 2
Identify typical uses of the storage media, including types of access (e.g. serial/sequential, direct/random) and access speeds 3
Describe the comparative advantages and disadvantages of using different backing storage media 4
Define the term backup and describe the need for taking backups 5
Describe the difference between main/internal memory and backing storage, stating the relative benefits of each in terms of speed and permanence

2. Section 1: Storage devices and media
Main Memory
Main memory (sometimes known as internal memory or primary storage) is another name for RAM (and ROM). Main memory is usually used to store data temporarily. In the case of RAM, it is volatile (this means that when power is switched off all of the data in the memory disappears).  Main memory is used to store data whilst it is being processed by the CPU. Data can be put into memory, and read back from it, very quickly. 
Memory is fast to access, but only holds data temporarily...
Backing Storage
Backing storage (sometimes known as secondary storage) is the name for all other data storage devices in a computer: hard-drive, etc.
Backing storage is usually non-volatile, so it is generally used to store data for a long time.
Backing storage devices are slower to access, but can hold data permanently...

3. Section 1: Storage devices and media
Serial / Sequential Access
A serial (or sequential) access storage device is one that stores files one-by-one in a sequence.  A non-computer serial access device that will be familiar to you is a VHS videotape. Because video is stored on a long piece of tape, when TV shows are recorded onto the tape, they go on one-by-one, in order..
If you want to watch a show that you recorded earlier, you have to rewind / fast-forward through all other shows until you find it.  The shows are only accessible in the same order that you recorded them. This type of one-by-one storage and access is called serial access.
Direct / Random Access
A direct (or ‘random’) access storage device is one that stores files so that they can be instantly accessed - there is no need to search through other files to get to the one you want. An example of a direct access device would be a DVD movie. Unlike the VHS videotape movie, you can jump to any scene on a DVD. All parts of the DVD are directly accessible. This type of file storage is called direct access.

4. Section 1: Storage devices and media
What is backing up of data?
A backup simply means making one or more copies of your data.
For example, if you have a folder of photos stored on the hard-drive of your laptop, you might back them up by copying them to a CD-R.
Why back up data?
If you delete a file by accident, your computer breaks, your laptop is stolen, or your business burns to the ground, having a backup copy means that you have not lost your precious data. You can recover your lost files and continue working. Most businesses use computers to store very important data (customer records, financial information, designs for products, etc.) If this data is lost, the business could possibly have to close. Backing-up business data is essential.
Magnetic
Optical
Solid state
Definition:
Magnetic storage media and devices store data in the form of tiny magnetised dots. These dots are created, read and erased using magnetic fields created by very tiny electromagnets.
In the case of magnetic tape the dots are arranged along the length of a long plastic strip which has been coated with a magnetisable layer (audio and video tapes use a similar technology).
Optical storage devices save data as patterns of dots that can be read using light. A laser beam is the usual light source. The data on the storage medium is read by bouncing the laser beam off the surface of the medium. If the beam hits a dot it is reflected back differently to how it would be if there were no dot. This difference can be detected, so the data can be read.
The term ‘solid-state’ essentially means ‘no moving parts’.  Solid-state storage devices are based on electronic circuits with no moving parts (no reels of tape, no spinning discs, no laser beams, etc.) Solid-state storage devices store data using a special type of memory called flash memory...
Examples:

5. Section 1: Storage devices and media
Fixed hard discs
Used to store operating systems, software and working data. Any application which requires very fast access to data for both reading and writing to. Not for applications which need portability. Used for online and real time processes requiring direct access. Used in file servers for computer networks
Portable hard discs
Used to store very large files which need transporting from one computer to another and price is not an issue. More expensive than other forms of removable media
Magnetic tapes
Any application which requires extremely large storage capacity and speed of access is not an issue. Uses serial access for reading and writing. Used for backups of file servers for computer networks. Used in a variety of batch processing applications such as reading of bank cheques, payroll processing and general stock control.
Optical backing storage media
such as CDs and DVDs
CDs tend to be used for large files (but smaller than 1Gb) which are too big for a floppy disc to hold such as music and general animation. DVDs are used to hold very large files (several Gb) such as films. Both CDs and DVDs are portable i.e. they can be transported from one computer to another. Both can be used to store computer data

6. Section 1: Storage devices and media
CD ROM/DVD ROM
Applications which require the prevention of deletion of data, accidental or otherwise. CDs used by software companies for distributing software programs and data; by music companies for distributing music albums and by book publishers for distributing
encyclopaedias, reference books etc. DVDs used by film distributors
CD R/DVD R
Applications which require a single ‘burning’ of data, e.g. CDs – recording of music downloads from the internet, recording of music from MP3 format, recording of data for archiving or backup purposes. DVDs – recording of films and television programs
CD RW/DVD RW
Applications which require the updating of information and ability to record over old data. Not suitable for music recording but is very useful for keeping generations of files. DVDs have between five and ten times the capacity of CDs
DVD RAM
Same properties as DVD RW but quicker access and data can be overwritten more easily. Similar to floppies in nature but has 3000– 6000 times more storage and uses optical technology
Blu-ray
Capacities of 25Gb, 50Gb and 100 Gb. Used for storing films (movies). 25Gb equates to 2 hours HDTV, 13hrs standard definition TV. It is possible to playback video on a disc while simultaneously recording HD video. (Will be) used for storage of PC data

7. Section 1: Storage devices and media
Solid state backing storage
Smallest form of memory, used as removable storage. More robust than other forms of storage. More expensive than other forms, but can be easily written to and updated
Memory sticks/Pen drives
Can store up to many Gb. Used to transport files and backup data from computer to computer
Flash memory cards
Used in digital cameras, palmtops, mobile phones, MP3 players