The DASD and Evolution of Storage Devices - Notes | CPSC 5155G, Study notes of Computer Architecture and Organization

Download The DASD and Evolution of Storage Devices - Notes | CPSC 5155G and more Study notes Computer Architecture and Organization in PDF only on Docsity! The DASD and Evolution of Storage Devices Rule 1: “Data processing requires data storage”. – I just made that up. Data were originally stored on paper media, first as written documents but fairly soon (Hollerith, late 19th century) the storage medium was machine–readable. In the 1950’s, New York Life Insurance Company was devoting an entire floor of its main building to the storage of punched cards. Something had to change. IBM quickly came out with two magnetic media for storing data the magnetic tape the DASD (disk) The acronym “DASD” stands for Direct Access Storage Device. Until recently, the standard disk drive was the only commercially viable example. We now have another very popular example, these USB “flash drives”. While different from standard disk drives, these are managed as if they were disk drives and are considered disk drives. Structure of a Large Disk Drive The typical large–capacity (and physically small) disk drive has a number of glass platters with magnetic coating. These spin at a high rate (7,200 rpm or 120 / second) This drawing shows a disk with three platters and six surfaces. In general, a disk drive with N platters will have 2N surfaces, the top and bottom of each platter. On early disk drives, before the introduction of sealed drives, the top and bottom surfaces would not be used because they would become dirty.