Physical Storage Media Cache-fastest and most costly form of storage;volatile;managed by the computer system hardware. Main memory: fast access (10s to 100s of nanoseconds;1 nanosecond 10-9 seconds) generally too small (or too expensive)to store the entire database capacities of up to a few Gigabytes widely used currently Capacities have gone up and per-byte costs have decreased steadily and rapidly (roughly factor of 2 every 2 to 3 years) Volatile-contents of main memory are usually lost if a power failure or system crash occurs. Database System Concepts-6th Edition 10.4 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 6 10.4 ©Silberschatz, Korth and Sudarshan th Edition Physical Storage Media Cache – fastest and most costly form of storage; volatile; managed by the computer system hardware. Main memory: fast access (10s to 100s of nanoseconds; 1 nanosecond = 10–9 seconds) generally too small (or too expensive) to store the entire database  capacities of up to a few Gigabytes widely used currently  Capacities have gone up and per-byte costs have decreased steadily and rapidly (roughly factor of 2 every 2 to 3 years) Volatile — contents of main memory are usually lost if a power failure or system crash occurs