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Storage

harddriveHard drives
When we turn the computer off, we don't want to lose all our files or we would have to do the work again! Neither to we want to reinstall software that we have already installed on our computer - that would use up a lot of our time. For these reasons, computer systems usually come with a hard disk. When you save files and applications to a hard disk, they are magnetically encoded onto disks so that when you turn the power off, the contents remain. When you power the computer back on, everything you saved onto the hard drive is still there for us to use. The jargon for devices that keep their contents even without power is 'non-volatile'. Hard drives are non-volatile devices. 

Opening programs and working with files
Hard drives (hard disks) aren't very clever! A hard drive is really just like a big suitcase. It can store lots of stuff but it can't actually do anything. Very importantly, it can't work directly with the brain of the computer, the CPU. If the CPU wants to open a program that's on the hard drive (or indeed any secondary storage device), it first has to make a copy of the program and then move that copy to its RAM (Random Access Memory). Then the CPU can work with the program in RAM. In just the same way, if you want to open a personal file you've stored, the CPU first has to copy the file from the hard drive to RAM. Only then, can you work on it. When you want to save any file, the file is copied from RAM to the hard drive. We can draw a model of this (remember 'abstraction')!CPU model

Secondary storage
Because hard drives don't work with the CPU, they are sometimes referred to as 'secondary storage devices'. RAM on the other hand is not a secondary storage device. It is often referred to as 'primary memory'. (In fact, RAM has got quite a few different names, including Immediate Access Storage, Memory and the Memory Unit.)

Common uses
The common use of a hard drive is to store all the files and the programs (including the operating system) in computer systems. They can also be used as a back-up device. You can buy external hard drives that just plug into a USB port. You can then use this just like you might use a pen drive. They can also be used to back-up whole computer systems. Some computers have not one but two hard drives. One hard drive is being used by the computer whilst the other one is being used to make exact copies (or 'mirrors') of the main hard drive. If the main hard drive fails - and all hard drives will fail one day - then the mirror hard drive can be used and no data is lost.

Technology used
We have already mentioned that hard drives use magnetism to store data. Other secondary storage devices use different technologies. For example, DVDs use lasers and optical technology to store data. Pen drives use something called 'solid state technology'. This just means that they use electronics to store data. Solid state devices are very interesting and very useful. They have no moving parts that can wear out unlike hard drives and optical drives and that also makes them fast by comparison. Solid state devices are getting physically smaller every year but can hold ever more data. They also require very little power to run compared to a hard drive.

Q1. Below is a table of other secondary storage devices. Copy it to Word or a similar word processing program and use then Internet to complete it. The first one has been done for you. Search for what each device is typically used for and you might find some surprising uses.

Device Optical, magnetic or
solid state?
Typical uses?

Pen drive

 

 Solid state Often used for making personal back-ups of files. They can be used to distribute files and applications by companies. You can run complete operating systems from them rather than using your computer's operating system and hard drive. They can be set up as 'rescue disks' in case your computer fails.

DVD drive

 

   

SD card

 

   

Blu-Ray

 

   

Magnetic tape

 

   

Q2. Why is data often 'compressed' before it is stored? What does 'data compression' mean?
Q3.
What is 'cloud storage'?
Q4. Find out the names of five companies or products that give you free cloud storage.
Q5. Do some research. discuss the pros and cons of cloud storage. Make sure you include any issues to do with privacy.

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