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From: "Michael Wahl, PicoQuant" <wahl AT pq DOT fta-berlin DOT NOSPAMPLEASE DOT de>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Protected Mode disk access
Date: Fri, 25 Jan 2002 19:56:02 +0100
Organization: PicoQuant
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To: djgpp AT delorie DOT com
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Eli Zaretskii wrote:
> 
> > From: "Tim Nicholson" <djgpp AT gizzy DOT co DOT uk>
> > Newsgroups: comp.os.msdos.djgpp
> > Date: Mon, 21 Jan 2002 17:45:50 -0000
> >
> > Am I correct in thinking the DJGPP switches from protected mode to real mode
> > to access the HDD and transfers data in 64K blocks (variable) via the DPMI
> > to and from DOS?
> 
> True, except that the default buffer size is 16KB, not 64KB.
> 
> > The reason for asking is that disk I/O seems much faster under Windows 98/ME
> > etc. and I am guessing this is partly because the whole thing is happening
> > in protected mode.
> 
> If you are comparing DOS and Windows, and see a significantly faster
> I/O on Windows, I suggest to install a large SmartDRV cache on the
> DOS machine, set it up to delayed-write operation, and try again.
> Chances are, you will see disk I/O that's as fast as on Windows.
> (Details can be found in section 3.9 of the DJGPP FAQ list.)
> 
> If you already have SmartDRV installed, please post the command line
> used to install it in AUTOEXEC.BAT.
> 
> > Does DOS (the one shipped with Win98) utilise the full capabilities of the
> > drive (i.e.. UDMA100 etc)?
> 
> Not DOS, BIOS.  DOS doesn't talk to the disk directly.


Ok, but can one get DMA under DOS/BIOS at all?