Memory Hierarchy Definition/Meaning:
For physically different kinds of memory, there are significant
differences in the time to access the contents of a particular location in a
memory, the volume of information that can be stored, and the unit cost of
storing a given amount of information. To optimize its use and achieve greater
efficiency and economy, memory is organized in a number of levels in a hierarchy
arranged as follows:
1. A single word held in each register of the processor; typically a word
contains 4 bytes. (This is sometimes not considered as memory.)
2. Groups of words within the cache; typically a single cache entry will hold 8
words (say 32 bytes).
3. Words within the main memory; groups of words are transferred between the
main memory and the cache.
4. Blocks of words held on permanently connected backing store. There are two
sublevels:
(a) pages of memory held on a swapping device - complete pages are transferred
between their backing store home and a page frame in main memory;
(b) complete files held on disk storage in the file store system.
5. Complete files backed up onto removable disks or magnetic tape within the
file store system.
See also memory management.
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