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HISTORY In the 1950s and the early 1960s single data Bit s were stored as magnetic charges in a magnetic Core Memory . Then the scientists at IBM in San Jose, California created a rotating drum that was coated in a magnetically polarizable film that could be used to store data by changing and sensing magnetic polarization. The drum was later superseded by disks, because of their lower mass and inertia. Reynold Johnson , an inventor who worked for IBM for many years, is said to be the "father" of the disk drive. The Random-access , low-density storage of disks was developed to complement the already used Sequential-access high-density storage provided by Magnetic Tape . Vigorous innovation in disk storage technology, coupled with less vigorous innovation in tape storage, has reduced the density and cost per bit gap between disk and tape, reducing the importance of tape as a complement to disk. AUDIO RECORDINGS In Music al and Audio data storage, the first devices were also drum shaped, called Phonograph Cylinder s, which were popularized by Thomas Edison . In the 1910s these were replaced as the dominant medium of Sound Recording by analogue disc records, commonly called '' Gramophone Record s'' (in British English ) or ''phonograph records'' (in American English ). From the 1950s through the 1980s , audio recordings were also done on Magnetic Tape media of several types, although the Vinyl Record remained the most popular medium for home use. These were mostly replaced by Compact Disc technology, where the data is recorded in a digital format as Optical information. This compact disc technology has been widely accepted, and data storage, using writable compact disks or CD-R devices is very common. ACCESS METHODS In disk storage, there are the two primary access methods. Block Storage (or ''raw disk storage'') means that the disk is divided into blocks which are addressed by number, like on a Magnetic Tape . File Storage contains an Abstraction of files and directories which can be addressed by name. Another access method, Content-addressable Storage (CAS) uses a hashing algorithm to refer to pieces of data. BASIC TERMINOLOGY
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