Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!pt.cs.cmu.edu!b.gp.cs.cmu.edu!Ralf.Brown@B.GP.CS.CMU.EDU
From: Ralf.Brown@B.GP.CS.CMU.EDU
Newsgroups: comp.sys.ibm.pc
Subject: Re: How to start an autobooting program without erasing memory?
Message-ID: <24b9da83@ralf>
Date: 11 Jul 89 11:31:15 GMT
Sender: ralf@b.gp.cs.cmu.edu
Organization: Carnegie Mellon University School of Computer Science
Lines: 32
In-Reply-To: <2245@astroatc.UUCP>

In article <2245@astroatc.UUCP>, brown@astroatc.UUCP (Vidiot) writes:
}In article <1186@atanasoff.cs.iastate.edu> jwright@atanasoff.cs.iastate.edu.UUCP (Jim Wright) writes:
}<In article <2236@astroatc.UUCP> brown@astroatc.UUCP (Vidiot) writes:
}<| Sorry, can't be done.  COMMAND.COM needs to start up all the programs because
}<| it sets aside pointers as to what memory is allocated for what.  Everything
}<| has to start from scratch when booting.  That goes for any computer.
}<                                                        ^^^
}<Wrong-o.  The Amiga supports a recoverable RAM drive.  Whether this is
}
}Wrong-o.  Read the original posting again.  The user was talking about TSRs,
}programs that reside in memory.  This is totally different than an area set
}aside for a RAM drive, which could be recovered.  With TSRs, interrupt vectors
}tend to be replaced and are lost when the system restarts and the COMMAND.COM
}is reloaded.

It is possible to write TSRs that can survive a reboot initiated by themselves,
but it would be hairy.  First, the TSR can't hook ANY interrupt vector used by
DOS itself, only BIOS and user vectors (it also has to make sure that those
vectors weren't hooked by DOS or another TSR which will disappear on rebooting--
that would really cause problems).  Second, it has to load itself at the top of
memory and modify the BIOS memory size word to make the memory it uses
unavailable to DOS.  Third, it has to reboot the system and load the boot
sector itself--doing a reset by jumping to F000:FFF0 will reset interrupt
vectors, and using the INT 19h reboot may also reset vectors (most likely
depends on the BIOS whether it does).

--
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