Appeal 2007-2127
Reexamination Control No. 90/006,621
A good definition of "concurrent" is found in Jean Bacon, Concurrent
systems: An integrated approach to operating systems (Addison-Wesley
Publ. Co. 1993), page 1:
Concurrent means 'at the same time'. . . . A concurrent system must
handle separate activities which are in progress at the same time. To
be a little more precise, we shall consider two activities to be
concurrent if, at a given time, each is at some point between its
starting point and finishing point. [Emphasis added.]
h. Multitasking in a single processor system
Concurrent execution of tasks (processes or threads) may be
implemented in two different ways. If there is a processor for each task, the
tasks may in fact be executing at the exact same time for true parallel
execution. If there is only one processor, the tasks must be switched back
and forth, which is called task or context switching, as described in Nguyen,
Advanced Programmer's Guide to OS/2, pages 9-10:
Task switching is the way in which multitasking is
implemented in a single processor system. The operating system
switches between the executing programs very quickly, distributing a
certain number of processor cycles to each. This is not the same thing
as true multiprocessing where each program would have its own
central processing unit. Nonetheless, multitasking by sharing the
resources of a single processor among several processes, each made
up of multiple concurrent threads, does possess great advantages over
executing programs sequentially.
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