What is the difference between a double density (DD) diskette, and a high density (HD) diskette?
Answer: The terms high density and double density are pretty confusing. A high density diskette can store 1.44 MB after being formatted. (It can hold about 2.0 MB before being formatted.) A double density diskette can only hold 720K of data, or half that of a high density diskette.
Sometimes, high density diskettes are referred to as HD/DD, which makes the difference a little more obvious. Double density diskettes are pretty much obsolete now, and it looks like HD diskettes are soon to follow.