An Operating Systems Vade Mecum

Glossary 351Waste. Unused space. External waste is outside of any virtual space. Internal waste isinside a virtual space but not needed. Overhead space is space occupied by tables neededfor translation. Also called fragmentation.Wild card. A convention that allows a number of files to be specified with one pattern.Winding latency. The time needed to wind a magnetic tape to the desired place.Window size. A parameter used in defining the working set of a process.Working directory. A directory that constitutes the environment for a process so thatthe process may refer to files in that directory by their local name.Working set. Pages belonging to a process that have been accessed by the process duringthe most recent w units of virtual time, where w is the window-size parameter.Working-set policy. A page replacement policy that restricts the number of processeson the ready queue so that physical store can accommodate all the working sets of readyprocesses.Workstation. A powerful single-user computer with a high-quality display, usually withsome local disk and a network connection.Write-behind. A policy that caches data blocks intended to be written out to devices inmain store and writes them when the device is available or when the cache entry isneeded for another purpose.Write-through. A policy that caches data blocks but writes them to the device wheneverthey are changed.