iAPX 286 Operating System Writers Guide 1983

GLOSSARYoutward call: the attempt to call a procedure in another segment whose DPL is numerically greater,than CPL.parallel table: a table whose entries have a one-to"one correspondence with the entries of a descriptortable, used to 'associate additional information with each descriptor.parallelism: concurrent execution of two or more tasks or devices.parameter validation: checking the attributes of parameters passed between procedures at differentprivilege levels to prevent protection violations or to detect exception conditions.PE bit: a Boolean in the MSWthat indicates whetherthe 80286 is running in real-address.modeor in'protected, virtual-address mode.Petri net graph: a notation for visualizing Petri nets. Petri nets are a mathematical tool for modelingsystems, first proposed by Dr. Carl Adam Petri in 1962.physical address: a 24-bit address, such as that used as a base address, capable of encomp~ssing theentire address spa~eof the 80286.physical segment: a segment as viewed by the processor, to be distinguished from "logical segme~t.';" ,PIC: programmable interrupt controller. See interrupt controller.pipes: a mechanism for intertask communi~ation used in the UNIX op~rating system. Each task viewsa communicatio~ channel as a file and uses READ and WRITE op~rations to r,eceive and send messages.placement policy: the algorithm for determining where in RAM to locate a segment.pointer: an item that specifies a memory location. A full o~ lorig pointer inciudes a selector; whichindirectly chooses a segment base address, and an offset value, which points to a specific address within~h!lt segment. An offset by itself is callt;d a short pointer.preemption: a dispatching process in which the operating system switches to another task even thoughthe current task has not requested any function that would cause it to wait. The operating system maypreempt one task in order to give othe~ tasks a share of CPU attention. ',.,., " , .prefix: one of several instruction codes that modify the function or the environment of the followinginstruction. iAPX 286 prefixes include the LOCK prefix, repeat prefixes, segment-override prefixes,and the ESCAPE prefix.present bit: a Boolean in a segment descriptor that indicates whether the segment is actuallly presentin RAM. In a virtual-memory system, the segment may have been evicted from RAM to create spacefor 'another segment.primitive: one of the operating-system operations made accessible to applications by some explicitmechanism. In the iAPX 286 'architecture, primitives are typically procedures with call gates in theGDTor LDTs.privilege: the right to access cettain portions of memory or to execute certain processor instructions.privilege level (PL): a: measure ,of privilege. In the iAPX 286, architecture, privilege is measured byintegers in the range 0-3, where 0 is the most privileged and 3 the least.Glossary-'8 121960-001