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 Blu-ray disks:27 GB to 54 GB 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-6th Edition 10.7 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 6 10.7 ©Silberschatz, Korth and Sudarshan th Edition 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 Blu-ray disks: 27 GB to 54 GB 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