Digital data refers to information stored as zeros and ones, while analog data refers to other storage methods. While digital data has largely supplanted analog data, some prefer analog storage techniques. Many analog records have been replaced by digital storage.
Digital data is stored as ones and zeros, which may be represented in a number of ways. A charged portion of a magnetic drive may represent a one, while an uncharged part might represent a zero. CDs use microscopic grooves to represent ones and zeros. There are no intermediate values with digital data which makes it easy to transfer between different media.
Analog data is a term created to differentiate it from digital data. Records and cassette tapes are forms of analog data storage; printed documents are considered analog as well. Analog data tends to be slower than digital data, but it can also be more precise. Since analog data allows for intermediate values, some believe it provides higher quality.
Some storage media can be used for both analog and digital data. Tapes are widely used for analog recordings in professional settings, but they can also be used to store ones and zeros for use with computers, and many companies still use tapes for hard drive backups.