Physical Storage Media(Cont.) Optical storage non-volatile,data is read optically from a spinning disk using a laser CD-ROM(640 MB)and DVD(4.7 to 17 GB)most popular forms Write-one,read-many(WORM)optical disks used for archival storage(CD-R,DVD-R,DVD+R) Multiple write versions also available(CD-RW,DVD-RW, DVD+RW,and DVD-RAM) Reads and writes are slower than with magnetic disk Juke-box systems,with large numbers of removable disks,a few drives,and a mechanism for automatic loading/unloading of disks available for storing large volumes of data Database System Concepts-5th Edition,Oct 23,2005. 11.7 ©Silberschat乜，Korth and Sudarshan
Database System Concepts - 5 11.7 ©Silberschatz, Korth and Sudarshan th Edition, Oct 23, 2005. Physical Storage Media (Cont.) Optical storage non-volatile, data is read optically from a spinning disk using a laser CD-ROM (640 MB) and DVD (4.7 to 17 GB) most popular forms Write-one, read-many (WORM) optical disks used for archival storage (CD-R, DVD-R, DVD+R) Multiple write versions also available (CD-RW, DVD-RW, DVD+RW, and DVD-RAM) Reads and writes are slower than with magnetic disk Juke-box systems, with large numbers of removable disks, a few drives, and a mechanism for automatic loading/unloading of disks available for storing large volumes of data
Physical Storage Media(Cont.) Tape storage non-volatile,used primarily for backup(to recover from disk failure),and for archival data sequential-access-much slower than disk very high capacity(40 to 300 GB tapes available) tape can be removed from drive storage costs much cheaper than disk,but drives are expensive Tape jukeboxes available for storing massive amounts of data hundreds of terabytes(1 terabyte 109 bytes)to even a petabyte(1 petabyte=1012 bytes) Database System Concepts-5th Edition,Oct 23,2005. 11.8 ©Silberschat乜，Korth and Sudarshan
Database System Concepts - 5 11.8 ©Silberschatz, Korth and Sudarshan th Edition, Oct 23, 2005. Physical Storage Media (Cont.) Tape storage non-volatile, used primarily for backup (to recover from disk failure), and for archival data sequential-access – much slower than disk very high capacity (40 to 300 GB tapes available) tape can be removed from drive storage costs much cheaper than disk, but drives are expensive Tape jukeboxes available for storing massive amounts of data hundreds of terabytes (1 terabyte = 109 bytes) to even a petabyte (1 petabyte = 1012 bytes)
Storage Hierarchy cache main memory flash memory magnetic disk optical disk magnetic tapes Database System Concepts -5th Edition,Oct 23,2005. 11.9 @Silberschatz,Korth and Sudarshan
Database System Concepts - 5 11.9 ©Silberschatz, Korth and Sudarshan th Edition, Oct 23, 2005. Storage Hierarchy
Storage Hierarchy (Cont.) primary storage:Fastest media but volatile (cache,main memory). secondary storage:next level in hierarchy,non-volatile, moderately fast access time also called on-line storage E.g.flash memory,magnetic disks tertiary storage:lowest level in hierarchy,non-volatile,slow access time also called off-line storage E.g.magnetic tape,optical storage Database System Concepts-5th Edition,Oct 23,2005. 11.10 ©Silberschat乜，Korth and Sudarshan
Database System Concepts - 5 11.10 ©Silberschatz, Korth and Sudarshan th Edition, Oct 23, 2005. Storage Hierarchy (Cont.) primary storage: Fastest media but volatile (cache, main memory). secondary storage: next level in hierarchy, non-volatile, moderately fast access time also called on-line storage E.g. flash memory, magnetic disks tertiary storage: lowest level in hierarchy, non-volatile, slow access time also called off-line storage E.g. magnetic tape, optical storage
Magnetic Hard Disk Mechanism track t spindle arm assembly sector s. cylinder c read-write head platter arm rotation NOTE:Diagram is schematic,and simplifies the structure of actual disk drives Database System Concepts-5th Edition,Oct 23,2005. 11.11 @Silberschatz,Korth and Sudarshan
Database System Concepts - 5 11.11 ©Silberschatz, Korth and Sudarshan th Edition, Oct 23, 2005. Magnetic Hard Disk Mechanism NOTE: Diagram is schematic, and simplifies the structure of actual disk drives