Editing Operating system (section)

===Multicomputer operating systems===
With [[multiprocessor]]s multiple CPUs share memory. A [[multicomputer]] or [[cluster computer]] has multiple CPUs, each of which [[distributed memory|has its own memory]]. Multicomputers were developed because large multiprocessors are difficult to engineer and prohibitively expensive;{{sfn|Tanenbaum|Bos|2023|p=557}} they are universal in [[cloud computing]] because of the size of the machine needed.{{sfn|Tanenbaum|Bos|2023|p=558}} The different CPUs often need to send and receive messages to each other;{{sfn|Tanenbaum|Bos|2023|p=565}} to ensure good performance, the operating systems for these machines need to minimize this copying of [[Network packet|packet]]s.{{sfn|Tanenbaum|Bos|2023|p=562}} Newer systems are often [[multiqueue]]—separating groups of users into separate [[Priority queue|queue]]s—to reduce the need for packet copying and support more concurrent users.{{sfn|Tanenbaum|Bos|2023|p=563}} Another technique is [[remote direct memory access]], which enables each CPU to access memory belonging to other CPUs.{{sfn|Tanenbaum|Bos|2023|p=565}} Multicomputer operating systems often support [[remote procedure call]]s where a CPU can call a [[Procedural programming|procedure]] on another CPU,{{sfn|Tanenbaum|Bos|2023|p=569}} or [[distributed shared memory]], in which the operating system uses [[virtualization]] to generate shared memory that does not physically exist.{{sfn|Tanenbaum|Bos|2023|p=571}}