From:	Glen Miner <gminer AT ca DOT newbridge DOT com>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Memory Protection
Date:	Fri, 15 Nov 1996 12:25:31 -0500 (EST)
Organization:	Newbridge Networks Corporation
Lines:	26
Message-ID:	<Pine.SUN.3.90.961115121752.21366A-100000@coop10>
NNTP-Posting-Host:	138.120.136.238
Mime-Version:	1.0
To:	DJ Delorie <dj AT delorie DOT com>
In-Reply-To:	<199611151720.MAA20713@delorie.com>
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

> > > > If I disable memory protection, will my program run faster?
> > > 
> > > No.
> > 
> > Really? I find this hard to believe. How does it detect memory 
> > violations? I would tend to think that it doesn't managed to determine 
> > this for "free", and would have to waste cycles in order to detect it.
> 
> Memory protection is handled by checking to make sure your accesses
> are within the segment boundaries.  When you "disable" protection in
> djgpp, all you are really doing is resizing the segments to cover all
> 4Gb of your virtual address space, so it is impossible to be outside
> the segment.  The CPU chip still does the computations required, but
> these rarely impact execution times - they're done in hardware.

Ahh, this makes sense now. I suppose my next question is: how does the
dosmem put/get  functions get around this? Do they resize before and 
after? Wouldn't this be painfully inneffeicient?

Peace
===[ Gabo / [ABC] : gaminer AT undergrad DOT math DOT uwaterloo DOT ca ]===================
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