multitasking OS
An operating system that can run one process for awhile, then switch to another one,
return to the first, etc. UNIX, VMS, MVS, TOPS, etc., are all multitasking systems. DOS
and Microsoft® WindowsTM are single-tasking operating systems. (Although MS-
WindowsTM can have more than one program active on the desktop, it does not do any
kind of preemptive context switching between them.)
NFS
An abbreviation for network file system--a kernel program that makes it possible to
access files across the network without the user ever knowing that the network was
involved.
page fault
The process of bringing in a page from disk when it is not memory resident. When a
program accesses a word in virtual memory, the MMU must translate that virtual address
into a physical one. If that block of memory is currently out on disk, the MMU must load
that page in.
page table
A table used by the MMU to show which virtual pages map to which physical pages.
POSIX
An acronym for portable operating system interface. This refers to a set of committees in
the IEEE that are concerned with creating an API that can be common to all UNIX
systems. There is a committee in POSIX that is concerned with creating a standard for
writing multithreaded programs.
Preemption
The act of forcing a thread to stop running.
preemptive scheduling
Scheduling that uses preemption. Time slicing is preemptive, but preemption does not
imply time slicing.
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