= Service requirement
{title2=$S$}
A <service requirement> is the amount of work a job needs from a server. <Queueing theory> often measures that work in units of <service time> at full server capacity. Under this normalization, a job with <service requirement> $S$ needs $S$ units of uninterrupted full-capacity service; waiting before service contributes to <queueing delay>, not to $S$.
If work is measured separately and a server supplies $r$ work units per second, a job requiring $w$ work units has full-capacity <service time> $w/r$. Six work units at two units per second require three seconds of service. Under <processor sharing>, interruptions or partial capacity can increase elapsed completion time without increasing the original <service requirement>. With normalized allocated capacity $c(t)$, completion occurs once $\int c(t)\,dt$ reaches $S$. A <residual service time> describes the unserved portion, rather than a fresh draw of the original <service requirement>.
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