Some additional mechanism must be added to provide for selective caching??”
a mechanism that avoids caching of I/O mapped addresses.
Some computers use both special I/O instructions and memory mapping. For instance, the PC architecture
uses memory mapping for the transfer of buffers to I/O controllers, and also uses I/O instructions to write to the
control registers of the interfaces.
PROCESSES AND SCHEDULING
The conceptualization of a running program has been refined as the field of computing has matured. Early
on, one spoke of running a job, or program. The program would be loaded on the computer, and it would run
to completion.
Later, computer scientists made the distinction between a program and a process. The program is the set of
instructions that will be executed when the program runs, and a process is an instance of a running program.
The difference is that the process maintains the state information about that execution of the program; it has
certain values for variables, for example, and a program location counter value at any particular moment, and
a certain section of the computer memory assigned to it.
In a multiprogramming environment (the name ???multiprogramming??? emerged before the widespread use
of the term ???process,??? for in today??™s language one would call it ???multiprocessing???), the distinction between
program and process becomes important.
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