Editing Computer multitasking (section)

== {{Anchor|COOP|Cooperative multitasking/time-sharing}}Cooperative multitasking ==
{{Main|Cooperative multitasking}}

Early multitasking systems used applications that voluntarily ceded time to one another. This approach, which was eventually supported by many computer [[operating system]]s, is known today as cooperative multitasking. Although it is now rarely used in larger systems except for specific applications such as [[CICS]] or the [[JES2]] subsystem, cooperative multitasking was once the only scheduling scheme employed by [[Microsoft Windows]] and [[classic Mac OS]] to enable multiple applications to run simultaneously.  Cooperative multitasking is still used today on [[RISC OS]] systems.<ref>
{{cite web
 |url = http://www.riscos.info/index.php/Preemptive_multitasking
 |title = Preemptive multitasking
 |date = 2009-11-03 |access-date = 2014-07-27
 |website = riscos.info
}}</ref>

As a cooperatively multitasked system relies on each process regularly giving up time to other processes on the system, one poorly designed program can consume all of the CPU time for itself, either by performing extensive calculations or by [[busy wait]]ing; both would cause the whole system to [[hang (computing)|hang]]. In a server environment, this is a hazard that makes the entire environment unacceptably fragile.