Date:	Tue, 30 Dec 1997 10:22:42 +0200 (IST)
From:	Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
To:	Dave Nugent <dave DOT nugent AT ns DOT sympatico DOT ca>
cc:	djgpp AT delorie DOT com
Subject:	Re: The Code DJGPP Generates
In-Reply-To:	<34A7E946.72F5@ns.sympatico.ca>
Message-ID:	<Pine.SUN.3.91.971230102223.577L-100000@is>
MIME-Version:	1.0

On Mon, 29 Dec 1997, Dave Nugent wrote:

> When I write and compile a program in DJGPP is it automatically 32
> bit?

Yes.

> If so, why do I not need to use a DOS Extender?

No.  You need a DPMI server.  If you run from Windows DOS box, you
already have one: the DPMI services are built into Windows.
Otherwise, get CWSDPMI, the free DPMI server for DOS which comes with
DJGPP (v2misc/csdpmi4b.zip from the same place you get DJGPP) and put
it somewhere along your PATH.  DJGPP startup code will automatically
load CWSDPMI if no DPMI services are available, and unload it when the
program exits.

> Does my program automatically switch to protected mode
> transparently?

Yes, the DJGPP startup code does that for you.

> 2 - Since it (DJGPP) requires a 386 or higher, should I assume that any
> program compiled with it will not run on a 286?

It won't run on a 286, since it needs 32-bit protected mode, which
286 doesn't support.

> Also does this mean it generates 386 instructions.

Yes, it generates 32-bit protected-mode code.

> 3 - If DJGPP uses 386 instructions, should I assume (that the same code
> written in DJGPP, and in Borlands Turbo C++ (Compiled in 286
> mode). that DJGPP's code will run faster?  Or is it only a small
> difference?

It depends on what your program does.  Typically, DJGPP produces code
that is faster than TC++, unless your program does a lot of disk I/O
or video RAM accesses.

> Is it only noticably quicker when doing things like 32 bit memory
> transfers?

About twice as fast as 286 TC code, and even more so if the original
TC code used far pointers.

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