The gigabyte (GB) is a unit which is used to specify the data capacity of a storage device and/or the data transfer speed of digital devices. It is used commonly to indicate the capacity of RAM and other storage devices, such as hard drives and memory cards.

Unfortunately, the exact value of a gigabyte can vary depending on which type of device is being described. This is because there are 2 different types of interpretation of gigabyte in use, decimal and binary.

The binary interpretation is mainly used to describe RAM, it is also used by some file storage systems within operating systems.

The decimal interpretation of the gigabyte is commonly used to describe hard drive capacities, as well as the capacity of memory cards, USB flash memory sticks and more. It is also usually used to describe the throughput (data transfer rate) of a device.

To give you an idea of how these different interpretations can affect the reported storage size of a device, or the data transfer rate, take a look at the values below:

PREFIX	DECIMAL VALUE	BINARY VALUE
GB	1,000,000,000 bytes (10⁹)	1,073,741,824 bytes (1024³, 2³⁰)

As you can see there is a disparity between the values described by each interpretation. This can create some confusion, for example, if you purchased a storage device which was advertised as having a certain storage capacity, due to the different interpretation your file system may indicate a smaller capacity. For instance, if you purchased a hard drive with an advertised capacity of 400GB, you may find your operating system quantifies the capacity as 372GB. For more on hard drive capacities click here

For more about bits and bytes see our guide to Binary Numbers.

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