Bits are grouped to form larger storage units, the most common of which is a byte. Bytes are made up of 7 and 8 bits, which, collectively, are also known as an octet. The word byte is a contraction of BinarY digiT Eight. The most important thing to remember here is that a byte usually holds one character—such as a number, letter, or symbol.
A megabyte (MB) contains 1,048,576 bytes. The prefix mega represents 1 million in the metric system and is used for file size, as well as for computer memory and hard disk capacity. A gigabyte (GB) contains 1,073,741,824 bytes. The prefix giga represents 1 billion in the metric system. You generally see gigabytes when talking about hard disk capacity. Large gigabyte hard drives now are the norm; you can purchase 40GB drives with no problem in a computer these days.