Invisible wrote:
> OK, that's what I wanted to know...

I have learned I have a knack for figuring out what technical question 
someone is *really* asking. I wish I knew why, so I could teach others 
to do it.

> (PS. Is there more than one interrupt level available? Or does it decide 
> which routine to call based on some other parameter?)

It depends on the CPU. Often there are multiple software interrupts 
available, but most OSes only use one, with a parameter passed in a 
register to indicate which one. Under MS-DOS, for example, it
was INT 21 (hex 21) to call DOS. The BIOS had a different interrupt 
(13?) for disks, and maybe one for the other stuff like video and all.

Learning how basic CPU stuff works is often very useful. Like, 
understanding that interrupts are nothing but polling the interrupt 
hardware wire at the start of each instruction can make you go "Oh! I 
see!" :-)

-- 
   Darren New / San Diego, CA, USA (PST)
     It's not feature creep if you put it
     at the end and adjust the release date.

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