Flash memory: EEPROM (electrically erasable programmable read-only memory).
Data in flash memory survive from power failure.
Reading data from flash memory takes about 10 nano-secs (roughly as fast as from main memory), and writing data into flash memory is more complicated: write-once takes about 4-10 microsecs.
To overwrite what has been written, one has to first erase the entire bank of the memory. It may support only a limited number of erase cycles ( tex2html_wrap_inline570 to tex2html_wrap_inline572 ).
It has found its popularity as a replacement for disks for storing small volumes of data (5-10 megabytes).
Magnetic-disk storage: primary medium for long-term storage.
Typically the entire database is stored on disk.
Data must be moved from disk to main memory in order for the data to be operated on.
After operations are performed, data must be copied back to disk if any changes were made.
Disk storage is called direct access storage as it is possible to read data on the disk in any order (unlike sequential access).
Disk storage usually survives power failures and system crashes.
Optical storage: CD-ROM (compact-disk read-only memory), WORM (write-once read-many) disk (for archival storage of data), and Juke box (containing a few drives and numerous disks loaded on demand).
Tape Storage: used primarily for backup and archival data.
Cheaper, but much slower access, since tape must be read sequentially from the beginning.
Used as protection from disk failures!
Flash memory: EEPROM (electrically erasable programmable read-only memory).
Data in flash memory survive from power failure.
Reading data from flash memory takes about 10 nano-secs (roughly as fast as from main memory), and writing data into flash memory is more complicated: write-once takes about 4-10 microsecs.
To overwrite what has been written, one has to first erase the entire bank of the memory. It may support only a limited number of erase cycles ( tex2html_wrap_inline570 to tex2html_wrap_inline572 ).
It has found its popularity as a replacement for disks for storing small volumes of data (5-10 megabytes).
Magnetic-disk storage: primary medium for long-term storage.
Typically the entire database is stored on disk.
Data must be moved from disk to main memory in order for the data to be operated on.
After operations are performed, data must be copied back to disk if any changes were made.
Disk storage is called direct access storage as it is possible to read data on the disk in any order (unlike sequential access).
Disk storage usually survives power failures and system crashes.
Optical storage: CD-ROM (compact-disk read-only memory), WORM (write-once read-many) disk (for archival storage of data), and Juke box (containing a few drives and numerous disks loaded on demand).
Tape Storage: used primarily for backup and archival data.
Cheaper, but much slower access, since tape must be read sequentially from the beginning.
Used as protection from disk failures!
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