iAPX 286 Operating System Writers Guide 1983

GLOSSARYintersegment reference: a reference to a location in a segment other than the segment containing thereference.intrasegment reference: a reference to a location in the same segment as the segment containing thereference.interlevel reference: an intersegment reference to a segment that has a different privilege level thanthat of the segment containing the reference.intertask transfer: a transfer of control flow to a task other that the current task.I/O-mapped I/O: a style of I/O interface in which I/O devices respond to addresses in an addressspace that is distinct from the memory address space. Special I/O instructions (IN, INS, OUT, OUTS)trigger I/O operations. The 80286 uses the M/IO pin to distinguish memory addresses from I/Oaddresses.I/O privilege level (IOPL): a two-bit item in the flag register of the 80286 that controls the currenttask's right to execute the I/O-related instructions IN, INS, OUT, OUTS, CLI, ST!, LOCK. A proceduremay not execute any of these instructions if CPL> 10PL.I/O subsystem: the portion of an operating system that deals with filing and I/O.IP (instruction pointer): an 80286 register that contains the offset of the instruction to be executedwithin the current code segment.kernel: that portion of an operating system that implements the most primitive of its functions.LDT register: an 80286 register that stores the selector, base address, and limit of the current LOT.limit: the field of a descriptor that defines the offset of the last byte of the segment.linkable module: an object module created by iAPX 286 translators, by the Binder, or by the Builderthat can serve as input to either the Builder or the Binder. A linkable module requires further processingbefore it can be executed.linking: the process of combining segments from one or more input modules and resolving referencesbetween modules. The Binder provides linking services for iAPX 286 program development.loadable module: an executable object module (usually created by the Builder or the Binder) that hasa format suitable for processing by a loader running under control of an operating system.loader: the task or procedures of an operating system that places an object module in RAM and preparesit for execution by the operating system and the processor.load-time: at the time a.task is loaded.local descriptor table (LDT): the descriptor table that contains descriptors that are (generally) privateto a given .task. Each task may have an LOT. A task can use only descriptors that are in its LOT or inthe GOT. The LOT protects tasks from one another.logical segment: the representation of a segment used by translators and program development utilitiesprior to the time when the segment is actually placed in physical memory.Glossary-6 121960·001