Your hard drive is the storage for your computer: it is where your programs, documents, photographs, music, videos etc. are stored.
Think of your hard drive like your kitchen cupboards: the more cupboards you have, the more you can store.
The size of a hard drive is measured in Gigabytes (GB) and Terabytes (TB).
1 Terabyte = 1024 Gigabyes
Most computers will come with a hard drive from 250GB to 1TB or more.
Laptops tend to have smaller hard drives than desktop computers.
A second hard drive can easily be added to a desktop computer. A laptop usually requires a larger hard drive to be swapped with the smaller one.
A tablet computer and some lighter laptops will have a special kind of hard drive called an SSD (Solid State Drive). These are drives without any moving parts. As they are more expensive, they tend to be smaller.
Many tablet computers will be sealed units and it might not be possible to open it to change the hard drive.
Games, photographs, music and videos will take up a lot of space on your hard drive. Documents do not tend to take up too much space.
Remember that your computer programs will also take up a lot of space on your hard drive.