X-Authentication-Warning: delorie.com: mailnull set sender to djgpp-bounces using -f From: "Tim Nicholson" Newsgroups: comp.os.msdos.djgpp Subject: Re: Protected Mode disk access Date: Mon, 21 Jan 2002 19:48:11 +0000 (UTC) Organization: BT Openworld Lines: 69 Message-ID: References: <1011635483 DOT 28296 DOT 0 DOT nnrp-08 DOT c1ed6b28 AT news DOT demon DOT co DOT uk> NNTP-Posting-Host: host217-35-53-59.in-addr.btopenworld.com X-Trace: helle.btinternet.com 1011642491 11536 217.35.53.59 (21 Jan 2002 19:48:11 GMT) X-Complaints-To: news-complaints AT lists DOT btinternet DOT com NNTP-Posting-Date: Mon, 21 Jan 2002 19:48:11 +0000 (UTC) X-Newsreader: Microsoft Outlook Express 6.00.2600.0000 X-MSMail-Priority: Normal X-Priority: 3 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000 To: djgpp AT delorie DOT com DJ-Gateway: from newsgroup comp.os.msdos.djgpp Reply-To: djgpp AT delorie DOT com Thanks, I can see the problems - Ho Hum :-) I thought that was the probably the case but it never hurts to ask. I take your point on the cache, but multi tasking and virtual machines are the real problems in our field. Tim wrote in message news:a2hlp7$g58$1 AT nets3 DOT rz DOT RWTH-Aachen DOT DE... > Tim Nicholson wrote: > > 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? > > Yes. Practically all I/O is done this by, in DJGPP. It has to be. > > > Is it not possible to access the HDD directly in protected mode via a FAT32 > > Library? > > A library wouldn't do it. To make sure you don't blow up the > underlying DOS, it would at least need a 16bit DOS driver counterpart > that informs DOS and its programs (smartdrv most notably), of what is > happening. Otherwise, you'ld almost certainly corrupt data. > > > - Does such a thing exist? and would it speed up disk I/O where > > reasonable quantities (several MB) of data was been transferred to > > and from the drive? > > Not by very much. That's what you have that several 10's of KB of > transfer buffer for, after all: to make sure the mode switch overhead > is as small as possible compared to the time the realmode call itself > (i.e. actual disk writing) takes. For linear reads from protected > mode, I don't think you can be much faster than DJGPP already is. > > Of course, it would still be crazy to implement a large database > management system in DJGPP... The tininess of the written blocks used > by such systems would drown your performance in modeswitch overhead. > > > 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. > > To some extent. There's also the fact that Windows talks directly to > the hardware, whereas DOS always goes via the BIOS, and thus can't use > some of the modern features, plus it may have to execute lots of code > that was and continues to be written with a 1980's MFM disk in mind. > > > going much faster! I can't use Windows or Linux because the code must be > > deterministic to meet certification requirments, besides, I like DOS! > > "Deterministic behaviour" and "caching" contradict each other to quite > some extent. > > > > > -- > Hans-Bernhard Broeker (broeker AT physik DOT rwth-aachen DOT de) > Even if all the snow were burnt, ashes would remain.