[Tutor] Running a script in the background

Alan Gauld alan.gauld at btinternet.com
Tue Sep 4 09:51:32 CEST 2012

On 04/09/12 01:26, Dwight Hutto wrote:

> But each OS(BIOS handler) has a way of providing/accepting instructions
> to the processor, which is constantly procedural. This has to have a
> terminal at some point.

No it doesn't. Most OS do not run in a 'procedural' way (by which I 
assume you mean sequential?) Most are event driven and that often at the 
hardware level. The processor has an interrupt mechanism which causes a 
section of code to run. The section chosen is determined by the 
interrupt number and results in a jump to a predefined address.
The interrupts are driven by hardware events with no software control.
Some interrupts are pre-emptive - they will stop any current processing 
and take control, others will wait for current processing to finish.
The processor will also have a software interrupt mechanism which does 
the same thing but is driven by an INT call in the software.

Operating systems from CP/M and DOS onwards are driven by interrupts
at the kernel level they do not sit in some kind of giant event loop 
looking for things to process.

> What is meant by behind a console, and running without a console, just a
> window system, and a file set that deals with instructions/errors based
> on BIOS input/output?

Again no, a terminal is an I/O mechanism. It reads input and displays 
output. The terminal does not process the commands it passes those to 
the program running inside it. Even the shell is not part of the 
Terminal, it just runs inside. And daemon programs do not use a terminal 
at all.

Alan G
Author of the Learn to Program web site

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