Friday, August 13, 2010


Musical and audio information was originally recorded by analog methods (see Sound recording and reproduction). Similarly the first video disc used analog recording. Analog recording has been mostly replaced by digital optical technology where the data is recorded in a digital format as optical information.

The first commercial disk storage device, that is the first commercial digital disk storage device, was the IBM RAMAC 350 shipped in 1956 as a part of the IBM 305 RAMAC computing system. Disk storage is now used in both computer storage and consumer electronic storage (e.g., audio CD and video DVD).

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.

Today disk storage devices typically have a single head that moves across a disk surface; earlier there were fixed head devices with multiple heads per surface but today they are no longer being manufactured. Movable head devices store more data per sensor and usually more per area of the medium. Fixed head devices avoid the seek time, while the head moves to the data.

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