Areal density is also called bit density. It is the amount of data that can be packed onto a storage medium. Areal densities are generally measured in gigabits per square inch (Gb/sq. inch).
The term is useful for comparing and measuring the efficiency in drive recording technology for different types of media, such as magnetic disks and optical disks. Current magnetic and optical disks have areal densities of several gigabits per square inch.
