What motherboard are you referring too ? I do not remember that quirk with an Asus P2B-F...but maybe my memory has a parity error ;p

Worked for me in the past on VIA KT266 and KT333 when AGP was primary, TGUI9680 secondary for second monitor under win98... however older PCI cards don't work in secondary mode, and you can't use them in DOS unless you disable AGP in CMOS setup, presuming you've got a half decent BIOS that lets you do that.

Also used a PCI card for a second monitor back in the Slot1/W98 days. IIRC only a handful of graphics chips could be used for it. No idea if it was a hardware, driver, or OS limitation. S3 Trio64 worked at least.

When the Geforce cards supporting more than one monitor came, I never looked back at dual card setups. No idea if it works better with more recent hardware/OS:es.

I don't know what it is, but I've had to get a dual-output card in order to use two displays at once.

The problem that I've had with at least two motherboards, if I wanted to use two video cards, is Windows 98 hanging when trying to access the Display settings in the Control Panel (i.e. the display positioning and the color depth.), if the BIOS is set to initialize AGP first. It also only works if the two display cards are by the same company, in the same era of production, with the same driver.

T-Squared wrote on 2023-07-27, 08:02:

I don't know what it is, but I've had to get a dual-output card in order to use two displays at once.

The problem that I've had with at least two motherboards, if I wanted to use two video cards, is Windows 98 hanging when trying to access the Display settings in the Control Panel (i.e. the display positioning and the color depth.), if the BIOS is set to initialize AGP first. It also only works if the two display cards are by the same company, in the same era of production, with the same driver.

Got some faint memory of having to set BIOS to initialize PCI graphics first too. No problems whatsoever using completely different graphics cards though. Had Voodoo Banshee, Riva TNT, TNT2 during that era, would guess I used all of them as the AGP card in a dual setup. IIRC I used the same old S3 Trio64 PCI card with all of them up until I got a GF256 with dual outputs, it only had to drive an 800x600 monitor for Photoshop and Freehand toolbars, IRC window, etc anyways. The mobos were an Asus P2B and later an Abit BH6.

For my motherboards, they were a Chaintech 6BTM and an ASUS P2B (the revision of which I can't remember.)

What video cards were they?

Next question: why do you need two monitors on a slot1 ? just curious 😁

At first, the dual monitor setup was for compatibility reasons, for a VR headset that used the VGA feature connector.

Unfortunately, it's any AGP and PCI video cards that I use. If it's not using the same driver and the AGP card is initialized first, the system freezes upon clicking the "Displays" option in Win98's Display Properties. (No response, nothing.)

So its not the video cards at all, its Windows 98 and the way it handles its drivers. Which lets face it was always flakey even back in the day and thats why we had to go out and buy dual head video cards.

There also seems to be a problem involving the GDI as well.

Yeah well there would be wouldnt there.
If you have a problem loading graphics drivers it will effect the GDI.

Though any non-trivial use of win 3.x through 9x/ME involves a GDI problem somewhere 🤣

Another thing to bear in mind is cards/displays might not initialize properly without a load seen on the VGA port, either a monitor plugged in or a dongle/resistor to fake it.

Okay, this is weird... I was JUST able to get both cards to work in the same system on BOTH hardware profiles (AGP-as-Primary, and PCI-as-Primary)... Maybe it's what card is active when you install Win98?

I don't know at this point. Maybe it was the version of Win98SE that I used?: https://archive.org/details/win98-2nd.

I have a GeForce 2 MX and a ET6000 card working together in Windows 98 (if I want to). I do not use it like that unless I want to compare monitors. I can just boot normally with AGP but I think you do have to connect a monitor before you boot or Windows will not correctly detect the output. Back in the day I had a colleague using two monitors on Windows 98 and that convinced me to buy a Matrox G400 (which is a single card) but the point is: he used two graphics cards so apparently it was a thing.

There is one thing that I've remembered, that I think was in the ASUS P3B manual. PCI/AGP seem to have hard-coded IRQs associated with them. There may have been an IRQ conflict, somehow.

In short, what other people have said in the past: swap your cards around in the slot? DO IT. That may be your problem.