Editing Central processing unit (section)

=={{anchor|PCM}}Performance==
{{further|Computer performance|Benchmark (computing)}}
The ''performance'' or ''speed'' of a processor depends on, among many other factors, the clock rate (generally given in multiples of [[hertz]]) and the instructions per clock (IPC), which together are the factors for the [[instructions per second]] (IPS) that the CPU can perform.<ref name="Freq">{{Cite web
 | title = CPU Frequency
 | work = CPU World Glossary
 | publisher = CPU World
 | date = 25 March 2008
 | url = http://www.cpu-world.com/Glossary/C/CPU_Frequency.html
 | access-date = 1 January 2010
 | archive-date = 9 February 2010
 | archive-url = https://web.archive.org/web/20100209041126/http://www.cpu-world.com/Glossary/C/CPU_Frequency.html
 | url-status = live
 }}</ref>
Many reported IPS values have represented "peak" execution rates on artificial instruction sequences with few branches, whereas realistic workloads consist of a mix of instructions and applications, some of which take longer to execute than others. The performance of the [[memory hierarchy]] also greatly affects processor performance, an issue barely considered in IPS calculations. Because of these problems, various standardized tests, often called [[benchmark (computing)|"benchmarks"]] for this purpose{{snd}} such as [[SPECint]]{{snd}} have been developed to attempt to measure the real effective performance in commonly used applications.

Processing performance of computers is increased by using [[multi-core processor]]s, which essentially is plugging two or more individual processors (called ''cores'' in this sense) into one integrated circuit.<ref name="tt">{{Cite web
 | title = What is (a) multi-core processor?
 | work = Data Center Definitions
 | publisher = SearchDataCenter.com
 | url = http://searchdatacenter.techtarget.com/sDefinition/0,,sid80_gci1015740,00.html
 | access-date = 8 August 2016
 | archive-date = 5 August 2010
 | archive-url = https://web.archive.org/web/20100805052158/http://searchdatacenter.techtarget.com/sDefinition/0,,sid80_gci1015740,00.html
 | url-status = live
 }}</ref> Ideally, a dual core processor would be nearly twice as powerful as a single core processor. In practice, the performance gain is far smaller, only about 50%, due to imperfect software algorithms and implementation.<ref>{{cite news|url=https://techspirited.com/quad-core-vs-dual-core|title=Quad Core Vs. Dual Core|newspaper=Tech Spirited |date=8 April 2010|access-date=7 November 2019|archive-date=4 July 2019|archive-url=https://web.archive.org/web/20190704093754/https://techspirited.com/quad-core-vs-dual-core|url-status=live |author1=Mlblevins }}</ref> Increasing the number of cores in a processor (i.e. dual-core, quad-core, etc.) increases the workload that can be handled. This means that the processor can now handle numerous asynchronous events, interrupts, etc. which can take a toll on the CPU when overwhelmed. These cores can be thought of as different floors in a processing plant, with each floor handling a different task. Sometimes, these cores will handle the same tasks as cores adjacent to them if a single core is not enough to handle the information. Multi-core CPUs enhance a computer's ability to run several tasks simultaneously by providing additional processing power. However, the increase in speed is not directly proportional to the number of cores added. This is because the cores need to interact through specific channels, and this inter-core communication consumes a portion of the available processing speed.<ref>{{Cite web |last=Marcin |first=Wieclaw |date=12 January 2022 |title=Factors Affecting Multi-Core Processors Performance |url=https://pcsite.co.uk/factors-affecting-multi-core-central-processing-unit-performance/ |website=PcSite}}</ref>

Due to specific capabilities of modern CPUs, such as [[simultaneous multithreading]] and [[uncore]], which involve sharing of actual CPU resources while aiming at increased utilization, monitoring performance levels and hardware use gradually became a more complex task.<ref>{{cite web|last1=Tegtmeier|first1=Martin|title=CPU utilization of multi-threaded architectures explained|url=https://blogs.oracle.com/solaris/post/cpu-utilization-of-multi-threaded-architectures-explained|publisher=Oracle|access-date=July 17, 2022|archive-date=July 18, 2022|archive-url=https://web.archive.org/web/20220718000821/https://blogs.oracle.com/solaris/post/cpu-utilization-of-multi-threaded-architectures-explained|url-status=live}}</ref> As a response, some CPUs implement additional hardware logic that monitors actual use of various parts of a CPU and provides various counters accessible to software; an example is Intel's ''Performance Counter Monitor'' technology.<ref name="intel-pcm">{{cite web |last1=Willhalm |first1=Thomas |last2=Dementiev |first2=Roman |last3=Fay |first3=Patrick |date=December 18, 2014 |title=Intel Performance Counter Monitor – A better way to measure CPU utilization |url=https://software.intel.com/en-us/articles/intel-performance-counter-monitor-a-better-way-to-measure-cpu-utilization |url-status=live |archive-url=https://web.archive.org/web/20170222150312/https://software.intel.com/en-us/articles/intel-performance-counter-monitor-a-better-way-to-measure-cpu-utilization |archive-date=February 22, 2017 |access-date=February 17, 2015 |website=software.intel.com}}</ref>