Physical Storage Media (Cont.) Magnetic-disk Data is stored on spinning disk,and read/written magnetically Primary medium for the long-term storage of data;typically stores entire database. Data must be moved from disk to main memory for access,and written back for storage Much slower access than main memory (more on this later) direct-access-possible to read data on disk in any order,unlike magnetic tape Capacities range up to roughly 400 GB currently Much larger capacity and cost/byte than main memory/flash memory Growing constantly and rapidly with technology improvements (factor of 2 to 3 every 2 years) Survives power failures and system crashes disk failure can destroy data,but is rare Database System Concepts-5thEdition,Oct 23,2005. 11.6 @Silberschatz,Korth and SudarshanDatabase System Concepts - 5 11.6 ©Silberschatz, Korth and Sudarshan th Edition, Oct 23, 2005. Physical Storage Media (Cont.) Magnetic-disk Data is stored on spinning disk, and read/written magnetically Primary medium for the long-term storage of data; typically stores entire database. Data must be moved from disk to main memory for access, and written back for storage  Much slower access than main memory (more on this later) direct-access – possible to read data on disk in any order, unlike magnetic tape Capacities range up to roughly 400 GB currently  Much larger capacity and cost/byte than main memory/flash memory  Growing constantly and rapidly with technology improvements (factor of 2 to 3 every 2 years) Survives power failures and system crashes  disk failure can destroy data, but is rare