Bits & Bytes

A guide to data storage capacities

Scared of killer-bytes? Threatened by mugger-bytes?  Frightened by terror-bytes?  Read on . . .

If you have bought or considered buying a computer, digital camera, MP3 or MP4 player, portable hard-drive, flash-memory card or any other form of digital device with storage you have probably read about how many ‘megabytes’ ‘gigabytes’ or even ‘terabytes’ it has.  If these terms are meaningless to you, our simple guide below may help.

On this page:  What it all means • Storage capacities explained • For the technically minded

What it all means

A byte is the smallest working unit of storage in a computer or other digital data storage device.  If you imagine a text document, each single letter or digit normally occupies one byte, so it takes four bytes to store the word ‘byte’{1}

Killer-bytes, mugger-bytes, terror-bytes, etc.

Imagine all the text, images, sounds and video clips stored on your computer and you can see that there are going to be millions of bytes of data.  It's inconvenient to have to write numbers with many zeros, so we use terms for groups of bytes.  By analogy, millimeters are useful for measuring small things but imagine if roadsigns had to give distances in mm?  So we use Metres and Kilometres instead.  The terms used for data storage (in ascending order of size) are:

• Byte (b)

• Kilobyte (Kb)

• Megabyte (Mb)

• Gigabyte (Gb)

• Terrabyte (Tb)

Storage capacities explained

How much storage you need depends, of course, on what you are intending to store.  Normal documents (letters, etc.) with no photos or logos take up very little space - perhaps just a few Kb - but audio files and photographs take up rather more and if you want to store movies you will need quite a lot of space.  The following table will help to give you an idea how much you can store:

The are, of course, approximate, as actual capacity will depend on many factors.  These values will apply to a typical user.

For the technically minded

We've deliberately not said exactly how many bytes there are in a kilobyte, etc.  That's because there are two different definitions in common usage (and a few others in less common usage) and we didn't want to cause confusion.  But if you really want to know, read on . . .

Many people and a lot of equipment manufacturers use the more obvious definition:

However, IT Professionals and technical purists will tend to use the original definitions, as set out when the computer industry began:

For most people the difference is immaterial, but if you buy a hard-drive rated as 1Tb, and then find your computer system reports that it has a capacity of 931Mb, don't worry - it's simply a different way of calculating terrabytes.

The Wikipedia 'Gigabyte' page is helpful if you need to read more.

{1} Technical purists are probably now saying "but what about Unicode and other variable-lengths formats?" We're intentionally simplifying the discussion here.  You can read more about Unicode on the Wikipedia.

{2} No longer sold at Moonbeams - found in older devices and included for comparison

We hope you find this information useful.  We have also tried hard to make sure it's accurate.  If you spot an error or think there's anything else that should be included here, please contact us.

Previous information item  Next information item  Information Index.