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Storage and File Structure (Physical Storage Media (2-Main memory…
Storage and File Structure
Classification of Physical Storage Media
Cost
Reliability
Speed
Physical Storage Media
2-Main memory
characteristics
Generally too small (or too expensive)
Volatile
Fast access
1-Cache
characteristics
Fastest and most costly form of storage
Small, managed by the computer system hardwar
Volatile
3-Flash memory
characteristics
Non-volatile
Reads are roughly as fast as main memory
writes are slow (few microseconds), erase is slower
4-Magnetic-disk
characteristics
Primary
medium for the long-term storage of data; typically stores
entire database
slower
access than main memory
Direct access
Non-volatile
5-Optical storage.
characteristics
Non-volatile
using a laser
Reads and writes are slower than with magnetic disk
6-Tape storage.
characteristics
Non-volatile
used primarily for backup (to recover from disk failure), and for archival data
Sequential access
Very high capacity
Magnetic Hard Disk Mechanism
Surface of platter divided into circular
tracks
Each track is divided into
sectors
A
sector
is the smallest unit of data that can be read or written
Performance Measures of Disks
Access time
Seek time
Rotational latency