Editing Central processing unit (section)

==Privileged modes==
Most modern CPUs have [[Supervisor mode|privileged modes]] to support operating systems and virtualization.

[[Cloud computing]] can use virtualization to provide '''virtual central processing units'''<ref>
{{cite book
| last1 = Anjum
| first1 = Bushra
| last2 = Perros
| first2 = Harry G.
| chapter = 1: Partitioning the End-to-End QoS Budget to Domains
| title = Bandwidth Allocation for Video Under Quality of Service Constraints
| chapter-url = https://books.google.com/books?id=3r3eBQAAQBAJ
| series = Focus Series
| publisher = John Wiley & Sons
| date = 2015
| page = 3
| isbn = 9781848217461
| access-date = 2016-09-21
| quote = [...] in cloud computing where multiple software components run in a virtual environment on the same blade, one component per virtual machine (VM). Each VM is allocated a virtual central processing unit [...] which is a fraction of the blade's CPU.
}}
</ref> ('''vCPU'''s) for separate users.<ref>
{{cite book
| last1 = Fifield
| first1 = Tom
| last2 = Fleming
| first2 = Diane
| last3 = Gentle
| first3 = Anne
| last4 = Hochstein
| first4 = Lorin
| last5 = Proulx
| first5 = Jonathan
| last6 = Toews
| first6 = Everett
| last7 = Topjian
| first7 = Joe
| chapter = Glossary
| title = OpenStack Operations Guide
| chapter-url = https://books.google.com/books?id=jQ5pAwAAQBAJ
| location = Beijing
| publisher = O'Reilly Media, Inc.
| date = 2014
| page = 286
| isbn = 9781491906309
| access-date = 2016-09-20
| quote = Virtual Central Processing Unit (vCPU)[:] Subdivides physical CPUs. Instances can then use those divisions.
}}
</ref>

A host is the virtual equivalent of a physical machine, on which a virtual system is operating.<ref>{{Cite web |date=2006 |title=VMware Infrastructure Architecture Overview – White Paper |url=https://www.vmware.com/pdf/vi_architecture_wp.pdf |url-status=live |archive-url=https://ghostarchive.org/archive/20221009/https://www.vmware.com/pdf/vi_architecture_wp.pdf |archive-date=2022-10-09 |website=VMware}}</ref> When there are several physical machines operating in tandem and managed as a whole, the grouped computing and memory resources form a [[Computer cluster|cluster]]. In some systems, it is possible to dynamically add and remove from a cluster. Resources available at a host and cluster level can be partitioned into [[Pool (computer science)|resources pools]] with fine [[Granularity (parallel computing)|granularity]].