chapter11storageandfilestructure-文庫吧
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【正文】 ? 寫稍微慢 ? 貴 ， ? 用于嵌入式設(shè)備 ， 數(shù)字相機 MP3 ? also known as EEPROM (Electrically Erasable Programmable ReadOnly Memory) 169。Silberschatz, Korth and Sudarshan Database System Concepts 5th Edition, Oct 23, 2022. Physical Storage Media (Cont.) ? Magicdisk 磁盤 ? Primary， longterm ， entire database. ? slower than memory ? directaccess – ? Hard disks vs floppy disks ? 100 GB currently ? Survives power failures and system crashes ? disk failure can destroy data, but is very rare 169。Silberschatz, Korth and Sudarshan Database System Concepts 5th Edition, Oct 23, 2022. Physical Storage Media (Cont.) ? Optical storage 光存儲 ? nonvolatile, data is read optically from a spinning disk using a laser 非易逝 ? CDROM (640 MB) and DVD ( to 17 GB) most popular forms ? Writeone, readmany (WORM) optical disks used for archival storage (CDR and DVDR) ? Multiple write versions also available (CDRW, DVDRW, and DVDRAM) ? slower than with magic disk ? Jukebox systems, 多個可移動盤 169。Silberschatz, Korth and Sudarshan Database System Concepts 5th Edition, Oct 23, 2022. Physical Storage Media (Cont.) ? Tape storage 磁帶 ? nonvolatile, used primarily for backup (to recover from disk failure), and for archival data 非易逝 ? sequentialaccess – much slower than disk ? 40 to 300 GB tapes available 大容量 ? cheaper than disk, but drives are expensive ? Tape jukeboxes available for storing massive amounts of data 海量磁帶庫 ? hundreds of terabytes (1 terabyte = 109 bytes) to even a petabyte (1 petabyte = 1012 bytes) 169。Silberschatz, Korth and Sudarshan Database System Concepts 5th Edition, Oct 23, 2022. Storage Hierarchy ?各層 ?存儲速度有數(shù)量級的差別 ?至少 10倍 慢介質(zhì)以廉價和容量而頑固地不肯退出歷史舞臺 169。Silberschatz, Korth and Sudarshan Database System Concepts 5th Edition, Oct 23, 2022. Storage Hierarchy (Cont.) 存儲分級 ? primary storage: 主存 ，快 ，易逝 ? secondary storage: next level in hierarchy, nonvolatile, moderately fast access time ? also called online storage ? . flash memory, magic disks 閃存，磁盤 ? tertiary storage: lowest level in hierarchy, nonvolatile, slow access time 第 3存儲 ? also called offline storage ? . magic tape, optical storage 磁帶光盤 169。Silberschatz, Korth and Sudarshan Database System Concepts 5th Edition, Oct 23, 2022. Magic Hard Disk Mechanism NOTE: Diagram is schematic, and simplifies the structure of actual disk drives 169。Silberschatz, Korth and Sudarshan Database System Concepts 5th Edition, Oct 23, 2022. Storage Access（存儲訪問） ? A database file is partitioned into fixedlen
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