The term gigabyte refers to 1024 megabytes.
The term gigabyte is commonly used to mean either 10003 bytes or 10243 bytes. The latter binary usage originated as compromise technical jargon for byte multiples that needed to be expressed in a power of 2, but lacked a convenient name.
A Byte is equal to 8 Bits. A Kilobyte is actually 1,024 Bytes depending on which definition is used. A Megabyte is approximately 1000 Kilobytes. A megabyte is a unit of information or computer storage equal to 1,048,576 bytes (Difference between kilobyte, megabyte and gigabyte).
A gigabyte -- pronounced with two hard Gs -- is a unit of data storage capacity that is roughly equivalent to 1 billion bytes. It is also equal to two to the 30th power or 1,073,741,824 in decimal notation. Giga comes from a Greek word meaning giant.