Hard disk drives are the main internal back store found inside a computer.
- They are rigid circular plates that have been magnitised (usually several disks)
- Each disk contains concentric tracks that are divided into sections where data is stored.
- Most disks store data on both sides
- The disk rotates at between 5,400 and 10,000 revolutions per minute (rpm) and the read/write heads float just above the surface of the disk
- If there is a problem with the hard drive, all of the data could be lost.
- External hard drives are quite affordable and a good option for storing large amounts of data (+ they are portable)
The main benefit is that they have a large capacity
Optical discs are the main external backing store.
- Optical discs include compact discs (CDs) and Digital Versatile Discs (DVDs).
- They store digital data as pits on the surface of a reflective disc.
- Data is read by a moving laser beam across the surface of the disc
There are three types of CD
Can only be used to read data ('Read-Only-Memory') - 650MB
Sold as blank CDs and can be written on once. After that they become CD-ROMs.
'Read and Write' - new data can be written on to the disc.
DVDs are like CDs, but hold more infomation/data - 8.54GB
CDs --> DVDs --> --> Blu-Rays In order of increasing capacity
Flash memory is often sold in pen drives/memory sticks.
- They're easy to connect to the computer through USB ports and hold between 1 and 32GB
- Memory sticks are tough and easily let you transfer data between computers
- Flash memory is a lot slower than a computer's RAM, but often fasted than a HDD.
- The main disadvantage is that they are small and can easily be lost/stolen and are more expensive then DVD-RWs
Flash memory is also used to make small memory cards
- These come in many different shapes and sizes
- Memory cards are used by digital cameras and some mobile phones and mp3 players.
- Many computers come with memory card slots, which means you can use them for reading/writing files, just like a memory stick
Magnetic tape can back up very large amounts of data.
- It is often used when large amounts of data needs to be backed up, it can store up to 800GB of data
- With magnetic tape, very large amounts of data can be stored cheaply, making them ideal for backing up hard drives or even a whole network
- Access is slow as read/write head can't go to exact piece of data, it has to search through all (serial/sequential access)
A floppy disk is a circular piece of magnetised metal protected by a hard plastic sleeve.
- The amount of data it can store is tiny - 1.4MB
- Accessing data is slow and they only last around 6 months
- ZIP disks are like floppies, but more reliable and solid. They can store up to 750MB, but are more expensive than floppies
- Floppy and ZIP disks are not used anymore, they have been replaced with modern day technology