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From: zech@leadsv.UUCP (Bill Zech)
Newsgroups: comp.sys.ibm.pc
Subject: Re: System boot
Summary: INT 19 is not the same as CTL_ALT_DEL
Keywords: system boot
Message-ID: <9312@leadsv.UUCP>
Date: 9 Jan 90 23:02:27 GMT
References: <945@excelan.COM> <77@qmsseq.imagen.com>
Organization: LOCKHEED, Sunnyvale, CA
Lines: 44

In article <77@qmsseq.imagen.com>, pipkins@qmsseq.imagen.com (Jeff Pipkins) writes:
> The int 19h vector is supposed to do a warm boot.  Like you, I have 
> experienced frequent hang-ups instead of boots when calling it.  I'm
> not sure why, either.
> 

There are really three types of boot operations on the PC.

COLD BOOT = power on /reset 
	This runs system diagnostics, executes the BIOS initialization,
	including setup of interrupt vectors, then boots DOS.

WARM BOOT = CTL_ALT_DEL
	This is just like a cold boot, except the diagnostics are
	skipped or abreviated.

INT 19
	This is a DOS boot ONLY.  The BIOS interrupts are *NOT*
	reset.  Note that INT 19 is a DOS interrupt, not a BIOS int.

Any TSR or driver which chains onto an interrupt vector must
intercept int 19, and reload the interrupt vectors with their
original values, before allowing DOS to handle the int 19.

If these resident programs don't do this, then when DOS reloads
(blowing away all your TSRs, etc.) the vectors will continue to
point at those no longer existing programs.  

Not all TSRs and drivers are friendly enough to do this, and that
is why the system will often crash when you execute an INT 19.
You might try removing all this stuff from your system and
try out the INT 19 with only one of them at a time to find out
which is the bad guy (or bad guys).

INT 19 is mainly used during startup after some initialization 
program runs to extened or modify the BIOS, allowing DOS to reboot with
a different BIOS configuration.

Some TSR's intercept INT 19 and then jump to the BIOS WARM start 
routines.

Hope this helps.

- Bill