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Wait state
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<h2 id="energy-conservation">Energy conservation</h2> <p>Wait states can be used to reduce the energy consumption of a processor, by allowing the main processor clock to either slow down or temporarily pause during the wait state if the CPU has no other work to do. Rather than spinning uselessly in a tight loop waiting for data, sporadically reducing the clock speed in this manner helps to keep the processor core cool and to extend battery life in portable computing devices. </p> <h2 id="alternative-meaning-on-ibm-mainframes">Alternative meaning on IBM mainframes</h2> <p>On <a href="/facts/IBM_mainframes/0kPkgADx">IBM mainframes</a>, the term <i>wait state</i> is used with a different meaning. A wait state refers to a CPU being halted, possibly due to some kind of serious error condition (such as an unrecoverable error during operating system to <a href="/facts/IBM_System%2f360_architecture/mKdceH2S">IPL</a>). A wait state is indicated by bit 14 of the <a href="/facts/Program_status_word/ejBFel3W">PSW</a> being set to 1, with other bits of the PSW providing a wait state code giving a reason for the wait. In <a href="/facts/Z%2fArchitecture/FcKYkGn9">z/Architecture</a> mode, the wait state code is found in bits 116-127.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Bubble_(computing)/e3Ee0yJg">Bubble (computing)</a></li> <li><a href="/facts/Cache_coherence/MhUD576q">Cache coherence § Coherence protocols</a></li> <li><a href="/facts/Consistency_model/a8Xphrs7">Consistency model</a></li> <li><a href="/facts/Cache_miss/gmJYN8wm">Cache miss</a> <ul><li><a href="/facts/Page_fault/0pzn9ByX">Page fault</a></li></ul></li> <li><a href="/facts/Multithreading_(computer_architecture)/ojEKsSNP">Multithreading (computer architecture)</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"IBM Knowledge Center". www.ibm.com. 9 December 2016. Retrieved 14 April 2017. <a href="https://www.ibm.com/support/knowledgecenter/SSLTBW_2.2.0/com.ibm.zos.v2r2.ieah700/iea3h7_Wait_State_Codes_in_z_Architecture_Mode.htm" target="_blank">https://www.ibm.com/support/knowledgecenter/SSLTBW_2.2.0/com.ibm.zos.v2r2.ieah700/iea3h7_Wait_State_Codes_in_z_Architecture_Mode.htm</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> </ol>