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What is Data Storage?

When we talk about `storing' data, we mean putting the data in a known place. We can later come
back to that place and get our data back again.

`Writing' data or `saving' data are other ways of saying `storing' data.

`Reading' data, `retrieving' data or…

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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…

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Accessing Stored Data
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Theory Notes
3. Storage Devices and Media
Accessing Stored Data

We refer to a collection of data stored in a computer system as a `file'. Files are often organised into

Whenever you click `Save' in an application, burn files to a CD-R,…

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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.


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Some storage media can only store a very limited amount of data, whilst others can store vast

Data storage capacity is measured in bytes (B).

A thousand bytes is known as a kilobyte (kB)
1,000B = 1kB

A million bytes is known as a megabyte (MB)

1,000,000B = 1MB…

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A million million bytes is called a terabyte (TB)

1,000,000,000,000B = 1TB

Even a very basic storage devices like a floppy disc can storage over a megabyte of data that's over 1
million letters or numbers!

And modern hard drives can store a terabyte of data or more that's more…

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Access speeds are measured in bytes per second (Bps).

Slow devices have speeds measured in thousands of Bps (kBps).

E.g. a floppy disc can save/read data at a speed of 60kBps

Fast devices have speeds measured in millions of Bps (MBps).

E.g. a harddrive can save/read data at a speed…

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Data is stored inside a hard-drive on rotating metal or glass discs (called `platters').

Fixed Hard Drive
A hard-drive built into the case of a computer is known as `fixed'. Almost every computer has a fixed

Fixed hard-drives act as the main backing storage device for almost all computers…

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Many portable music players (such as the iPod classic) contain tiny hard-drives. These miniature devices
are just not much bigger than a stamp, but can still store over 100MB of data!

Magnetic Tape
Magnetic tape is a large capacity, serial access medium. Because it is a serial access medium, accessing…

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Removeable Media Magnetic Discs

Floppy Disc
A removable, portable, cheap, low-capacity (1.44MB) storage medium. Floppy discs are random
access devices used for transfer small amounts of data between computers, or to back-up small files,
etc. Access times are slow.

Almost every PC used to have a floppy disc drive. These…





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