An Operating Systems Vade Mecum

Glossary 347Serially reusable. A resource that may be granted to a process after it has been used byanother.Service. (1) To service an interrupt is to give the next data to or accept the last set ofdata from a device that has interrupted because it has finished the previous transput. (2)To service a device is to service the completion interrupt for that device.Service call. A request that a running process makes of the kernel to acquire or release aresource or to perform transput. Service calls always switch context to the kernel.Service rate. The rate at which processes can be executed, usually represented by β.The expected time to service a single process is 1 / β.Session. A period of interactive use lasting from logon to logoff.Short-term scheduling. Any policy that determines the order in which ready processesare executed. The short-term scheduler is also called a dispatcher.Shuffling. Moving segments within physical store to coalesce free space into one piece.Also called compaction.Simplex. A kind of communication line where data travels in only one direction. (SeeFull duplex and Half duplex.)Simulation. Deriving the behavior of a collection of interrelated objects by usingrandom-number generators to make probabilistic decisions and measuring a large numberof samples.Skewing. Spacing consecutive blocks of a file a few sectors apart on a disk.Space. A resource that the operating system allocates among the various processes thatcompete for it. Space is the ability to store information, whether in main or backingstore.Spin switch. A generalization of the non-alternating switch to n conflicting activities.Also called Spin lock.Split. To create the virtual space of a new process by copying an existing process. (SeeLoad.)Spooling system. A simple operating system that collects jobs on a disk until it can runthem and stores output on a disk until it can print it, but runs only one job at a time.Stable storage. Storing data redundantly on the disk so that any single failure results ina readable version of the data.Stack property. A property of a page-replacement algorithm that prevents anomalies.At each point in any page-reference string, the set of pages that would be in an n -pageframemain store is a subset of those that would be in an (n + 1)-page-frame main store.Startup phase. The time after a process enters the ready list from the main-store waitlist until it has acquired its working set.Startup phase conflict. The situation in which several processes are simultaneously instartup phase.