Editing Cache coherence (section)

=== Snooping ===
{{main|Bus snooping}}
: First introduced in 1983,<ref>{{Cite journal|title=Ravishankar, Chinya; Goodman, James (February 28, 1983). "Cache Implementation for Multiple Microprocessors"|url=https://www.cs.ucr.edu/~ravi/Papers/NWConf/ravishankar_83.pdf|journal=Proceedings of IEEE COMPCON: 346–350.}}</ref> snooping is a process where the individual caches monitor address lines for accesses to memory locations that they have cached.<ref name=":3" /> The ''write-invalidate protocols'' and ''write-update protocols'' make use of this mechanism.

: For the snooping mechanism, a snoop filter reduces the snooping traffic by maintaining a plurality of entries, each representing a cache line that may be owned by one or more nodes. When replacement of one of the entries is required, the snoop filter selects for the replacement of the entry representing the cache line or lines owned by the fewest nodes, as determined from a presence vector in each of the entries. A temporal or other type of algorithm is used to refine the selection if more than one cache line is owned by the fewest nodes.<ref>Rasmus Ulfsnes (June 2013). [http://www.diva-portal.org/smash/get/diva2:649627/FULLTEXT01.pdf "Design of a Snoop Filter for Snoop-Based Cache Coherency Protocols"] {{Webarchive|url=https://web.archive.org/web/20140201160231/http://www.diva-portal.org/smash/get/diva2:649627/FULLTEXT01.pdf |date=2014-02-01 }} (PDF). ''diva-portal.org''. Norwegian University of Science and Technology. Retrieved 2014-01-20.</ref>