An Operating Systems Vade Mecum

Glossary 343Partition. A fixed region of main store used as a virtual space. The partition methodwas supported by the IBM 360 and used in the OS/360 operating system.Password. A secret combination of symbols. Subjects that know a password haveaccess to the objects it protects.Path expression. A syntax for specifying synchronization information.Path name. Part of a full file name that specifies the directory in which the file is found.Pattern. A string that represents a set of file names.Penalty ratio. The ratio of response time to required time for a given process,represented by P. P is always greater than or equal to 1. Also called Execution time multiplicationfactor. (See Response ratio.)Permanence. A property of transactions that once one completes successfully, theresults of its operations will never be lost.Personalized shorthand. A phrase acceptable to the command interpreter that isexpanded to a different phrase as established by the user.Phase change. When a program leaves one region of locality and enters another.Physical. The raw materials of an abstraction, typically actual hardware, as opposed to avirtual view of it. (Opposite of Virtual.)Pipe. An inter-process communication device that appears like a file opened for readingby one process and writing by another.Platter. A part of a disk pack, divided into tracks.Policy. A way to choose which activities to perform. (See Mechanism.)Polling. Periodically checking the status of a physical or virtual device, usually to detectcompletion of a transput operation.Pool. A pool page replacement method chooses a page to swap out from a pool of availablepage frames. (See Local and Global.)Port. A virtual device through which processes communicate.Port capability. Permission to read or write to a particular port. This permission can betransmitted in messages.Port file. A file that allows processes that open it to communicate with each other.Preemption. Reclaiming a resource from a process before the process has finished usingit.Prefetching. Bringing pages into main store before they are needed by a process inorder to avoid wasting time servicing page faults or file transput requests. (See Locality.)Present field. A field in the translation table set by the software when a page or segmentis swapped in.Privilege. Access right.Privileged state. See Processor state.