Magnetic Tape : It is a plastic ribbon coated with a magnetizable material. it may be a large rill in the form of cassette. Data is stored in the form of tiny segments of magnetized portion on the surface of the material. As the receiving reel turns with pool of the tape in front of read/write head. Data can be retrieved by sensing the present and absent of magnetic spots on the tape. Records are written on after another serially with a gap. The gap between records are called Inter Record Gap (IRG). Tapes comes in a number of forms including half inch wide tape, 1/4 inch wide tape. It is least expensive and durable, used for backup. It is not suitable for data files that need to be revised or update often because it store data in a sequential manner. magnetic tape use two reels. supply reel and take-up reel and the tape moves from the supply to take up reel. The tape is divided in vertical columns (frame) and horizontal rows (channel or tack). The data is stored in a string of sucessive columns and frames with one data per frame.
Magnetic disk : It is most widely used and popular storage medium for direct access secondary storage. They offer high storage capacity ,reliability and have the capability to access the stored data directly. it is a circular platter of plastic/metal coated with magnetizble material. Data is represented as magnetized spots on a disk. One of the key component of a magnetic disk is conducting coil named as head. The perform job of reading and writing on the magnetic surface. The head remains stationary while the disk rotates below it for reading and writing operations. Writing data on the disk is accomplished by converting electrical impulse from the processor into magnetic spot on the disk. The data in a magnetic disk can be erased and reused virtually infinity. the capacity of magnetic disk is 1MB to several Megabytes.
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