Re: A basic question about running a program

From: Chris \( Val \) (chrisval_at_bigpond.com.au)
Date: 04/07/04 

Date: Thu, 8 Apr 2004 01:35:09 +1000

"Gary Labowitz" <glabowitz@comcast.net> wrote in message
news:B9adnYWbCLAegOnd4p2dnA@comcast.com...
| "osmium" <r124c4u102@comcast.net> wrote in message
| news:c511j4$2nocad$1@ID-179017.news.uni-berlin.de...
| > Tony Johansson writes:

[snip]

| And I add....
| Only one program at a time is ever "running" in a single processor
| system. You can think of multiprogramming as the processor switching
| back and forth between "running" programs. The program that does the
| switching (giving up control of the processor while some other program
| in "running") stops "running" until the switched-to program gives up
| control voluntarily or is interrupted by the hardware, usually with a
| timer or I/O interruption. Then the switching program gets control
| again and switches to another program, answers pending user interface
| actions, etc.
|
| HOWEVER, even this "running" program (called the operating system in
| most cases) can give up control of the processor and enter what is
| know as the wait-state. At that point one could argue that NO program
| is "running." And you'd be right. The hardware, however, keeps right
| on ticking and responding to hardware interruptions (like the user
| hitting a key, or a timer interruption, or an external signal from
| another system, etc.). There are several standard interruptions of
| this type: hardware, I/O, timer, external. If you consider the clock
| chip cycling as "running" then that prom is running -- but no
| memory-resident program is.

This is all off topic, of course, but I think
Leor has summed it up perfectly with respect to
time-slicing, and the various scheduling models
employed.

Cheers.
Chris Val

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