The correct answer is D. Quad-density (QD) diskettes are double-sided diskettes with double the number of tracks per inch than double-density diskettes. This means that they can store twice as much data as double-density diskettes.
A. Double-sided diskettes have two sides that can be used to store data. This means that they can store twice as much data as single-sided diskettes.
B. Double-density diskettes have a higher storage density than single-density diskettes. This means that they can store more data on the same amount of space.
C. Tracks are concentric circles on a diskette that data is stored on. The number of tracks per inch (TPI) is a measure of the storage density of a diskette. A higher TPI means that more data can be stored on the diskette.
E. None of the above is not the correct answer. Quad-density diskettes are double-sided diskettes with double the number of tracks per inch than double-density diskettes.