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Re: [Qemu-devel] Old DOS under Qemu

From: jeebs
Subject: Re: [Qemu-devel] Old DOS under Qemu
Date: Thu, 12 May 2005 11:25:22 -0500


> >From version 5 on up, I only have a few problems (Which I've already
> > reported.)

>I want to come back on the last item. I have made images of my 15y old 720k
>floppies, and jumped back to 1991 this morning.

The only problems I've noticed with newer DOS's are (right off the top of my 

1) mouse driver problem failing.  (In the Ghost backup floppy.  Standard 
microsoft driver.)  Also, Ghost itself fails with the same error.  This disk 
definetly works under real hardware because I use it.

2) DrDos 7.03 (?) having trouble detecting the <enter> key during 
installation.  Or maybe the floppy change...

3) Mouse driver in FreeDos hangs up.

4) Some of them saying that A20 is already enabled.  That shouldn't start up 
like that.  I think it's supposed to be disabled by default.

5) The mouse rate on my host wasn't always exactly like it originally was. 
That was a big problem a few months ago.  I had a 'dirty' copy of XP and was 
using the latest Logitech mouse driver.  I suspect it was the mouse driver, 
actually.  I recently reinstalled and I'm using the default driver in XP, 
and most of those problems immediately disappeared.  However, there have 
been a couple times when I'd shut qemu down and my host mouse driver seemed 
just a wee bit slower than it should be.  It'd test it, and then reset the 
speed and test it again, and it seemed like it was a speed mark too slow.

But, for the moment, I'm willing to say it was my imagination.  It must have 
been the Logitech mouse driver causing so much problem before.  (Whatever 
the cause though, it was *definetly* repeatable.  It wasn't an occasional 

There may have been a few other issues that I've reported, but right off 
hand I can't remember them.  Plus all the standard stuff, such as the cd 
change problem, etc. etc.

>- floppies 720k: ok. The catch to format them is to either quick format 
>not in high density. Inside win3.00a, it works like a breeze.

Qemu has problems dealing with older size floppies.  It should check the 
size and use that as an indicator what it's supposed to be.  (Or add yet 
another command line switch.)

Qemu could get fancy and start specifying all storts of options for custom 
disks, etc. but I don't know if the BIOS would support them or not.  (Shame 
the bios isn't written for easier hacking.  And it's a shame that qemu & 
bochs can't handle a larger bios so it could be extended, config screens 
added, etc. etc.)

Probably be easier to just check for disk sizes of 160k, 180k, 320k, 360k, 
720k, 1.2m, 1.44m, 2.88m, 820k, 1.72m and 1.68m  and set the hardware type 
accordingly at startup.  (Again, I don't know what sizes the bios can 

(Actually, if you check the disk sizes, you may have to allow a few k-bytes 
either way, since some disk images may not be the exact byte size, even 
though they should be.)

>I've seen no problem whatsoever. Do you want my bins jeebs ?

Thanks for the offer, but I already own Dos 5 and Win300a (although 
admittedly the images I'm using came from a friend, since I no longer have a 
5.25" floppy, and didn't make images of them back then.)

I am still looking (for qemu testing purposes, of course, since I wouldn't 
try to install this on my real computer[laugh]) for a valid, known good copy 
of ms-dos 3.3, pc-dos 4.01, and pc-dos 6.10.  And maybe pcdos 7 and 2000. 
And I wouldn't be opposed to Win/286 or Win/386 either.

The warez copies I have could either be damaged or hardware specific.  It 
wasn't uncommon for dos 3.x to be modified for a specific brand of computer 
or even a specific machine.  And although it's interesting that the copies I 
have behave differently in Bochs than in Qemu, I'm definetly willing to say 
that due to their warez nature, the results may not be accurate or 

I guess, realistically, that my testing old OS's may not really help qemu 
development all that much, but since my home computer is older and not as 
fast as most people's, I don't really want to spend hours and hours and 
hours trying to install XP or Win2k3 or something, just to have it fail.  If 
the qemu accelerator modules worked under Windows (and actually improved the 
speed, since qvm86 seems to slow qemu down!), then I might.

But for now, testing older stuff is all that I have time for.

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