Mail Archives: djgpp/2012/05/18/18:15:21

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From: Rugxulo <rugxulo AT gmail DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: incompatible
Date: Fri, 18 May 2012 14:48:18 -0700 (PDT)
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On May 18, 1:40pm, Georg <dos DOT  DOT  DOT  AT googlemail DOT com> wrote:
> On May 18, 8:08pm, Ster DOT  DOT  DOT  AT aol DOT com wrote:
> > is 64 bit the end or do you think we will get 256 ?
> > and maybe completely different incompatible processors !?
> I think there are already processors available which use more than
> 64bit - but not from Intel I guess.

I think 64-bit is here to stay for quite a while (famous last words).
All competing processors seem to have already migrated to 64-bit as

This doesn't count instruction extensions like AVX, of course, which
use 256-bit registers.

> One of the reasons for 64bit is that you can address more than 4GB of
> memory.

32-bit Windows typically only let you access approx. 3.1 GB of RAM,
maximum. Actually, on this computer here, the max I can allegedly use
(in any 32-bit OS) is 2.9 GB. Memory holes, address space, etc.
(boring). Linux may be able to use up to 4 GB in 32-bit mode, but I'm
not sure.

MS does not support PAE access at all (thanks to "driver bugs"), so
they are indirectly forcing us to all use Win64 to access more RAM.
With PAE, you could theoretically access up to 64 GB (but not all at
once, would have to page in and out I guess). AMD64 originally was
only 40-bit (1 TB) of RAM capability, but latest versions are 48-bit
(256 TB).

Long story short, you've already been seeing much more 64-bit editions
of Windows than otherwise because of this, but Win8 (finalized later
this year) will supposedly still have a 32-bit edition (at least
judging from their previews).

> The previous processors like 386 provided a VM86 mode to support the
> use of several 16bit applications while in 32bit mode. This is what
> the Windows XP command window is based on and makes it work so well.

XP is very good for DJGPP stuff (esp. thanks to CWS' fixes), but it
still has bugs and some annoying gfx limitations. Though it's still
far far better than Vista or 7, ugh. Too bad XP is deprecated.

> The 64bit processor comes without VM386 mode. So when Windows switches
> to 64bit mode it has no way to run a command window in VM386 or VM86
> mode. This has to be emulated in software completely and that is
> provided by e.g. VirtualPC.

There is partial 16-bit pmode support, allegedly, but I guess MS never
bothered. Well, their Win16 stuff was all based atop DPMI anyways, so
if there is no DOS, I guess there is no Win16.

You can run DOS stuff atop 64-bit Windows, almost natively, with VT-X.
Otherwise I don't know, my limited experience without VT-X proves that
software only emulation isn't good enough (too buggy). If you don't
have VT-X, your best luck is dual booting (to either native DOS or
Linux with DOSEMU).

> A 64bit processor will usually boot in 16bit mode. So if you boot from
> a CD with DOS and have a FAT32 partition on your hard disk you can
> work in real mode DOS.

MS is basically doing away with NTVDM for various reasons that I can't
understand. My guess is that they expect Hyper-V atop VT-X to be a
better successor.

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