Gigabyte is a measurement for the amount of data. The unit symbol for the gigabyte is GB. The gigabyte is a multiple of the unit byte for digital information. Therefore, one gigabyte is 1000000000bytes.
Bandwidth is the amount of data that can be transmitted in a fixed amount of time. This is similar to measuring the capacity of a water pipe at liters per second.
For digital devices, the bandwidth is usually expressed in bits per second(bps)
When spelled Mbps, short for megabits per second, a measure of data transfer speed (a megabit is equal to one million bits). Network transmissions, for example, are generally measured in Mbps.
