Does anyone have experience with running two PCI cards? I have a newer card for 3D games under Windows 95/98, but thought about adding an older card for better DOS/Windows 3.1 compatibility. What would happen if I boot into DOS with two cards installed?
asdf53 wrote on 2022-03-28, 14:06:Does anyone have experience with running two PCI cards? I have a newer card for 3D games under Windows 95/98, but thought about adding an older card for better DOS/Windows 3.1 compatibility. What would happen if I boot into DOS with two cards installed?
PCI+PCI videocards configuration is compatible with Win98 or newer operating systems. Othervise one of videcards will be primary and works, secondary will be disabled or conflict with primary videocard.
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I see. Maybe you could put them into PCI slots in such a way that the DOS card is recognized as primary, and then in Windows 95 device manager, disable the first card to make it use the second one? Would that work?
asdf53 wrote on 2022-03-28, 15:11:I see. Maybe you could put them into PCI slots in such a way that the DOS card is recognized as primary, and then in Windows 95 device manager, disable the first card to make it use the second one? Would that work?
No, this way not works.
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It's been a while since i ran dual PCI cards. This was in an AGP 440BX system, with an AGP card too. Three head. IIRC, one of the PCI cards i tried insisted on being the primary, the other one and the AGP were secondary. I went to a dual setup because i wanted the AGP as primary.
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asdf53 wrote on 2022-03-28, 15:11:I see. Maybe you could put them into PCI slots in such a way that the DOS card is recognized as primary, and then in Windows 95 device manager, disable the first card to make it use the second one? Would that work?
Only one card can use the classic VGA address ranges, i.e. ports 3C0-3DF and memory A000-BFFFF. The PCI standard doesn't provide a generic way to assign these resources to a specific VGA card, so only one VGA-compatible card may be "enabled" on the PCI bus at a time. The PCI-to-PCI bridge standard on the other hand allows to select which bridge may forward VGA cycles. So If you have a AGP graphics card connected to the AGP bridge that is part of the host bridge, classic VGA can be shut off in that bridge while other cycles (linear frame buffer, memory mapped I/O) is kept enabled. This enables running an AGP card and a PCI card at the same time - provided the AGP card and its driver support to not use the classic address ranges. Most PCI and nearly all AGP graphics cards are designed in a way that you can operate them perfectly without using the classic ("legacy") address range.
There is no official provision to switch which cards provides VGA services while DOS is running, though. Switching the card that provides VGA services would mean you need to replace the video BIOS on the fly, which is unsupported.
Some Mach64 cards have a jumper on them to disable the VGA addresses etc., and I guess it is specifically for having several cards in the system.
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Trident TGUI 9680 1/2MB PCI cards handle being a 2nd or 3rd card under 98SE and most other cards will let them. I've had one in addition to a V3 and a GF2 before. Don't think direct draw works on the secondary though.
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Thanks for your replies and the helpful insights, everyone. Sadly I do not have an AGP slot, it's an older Socket 7 board. I understand that you can only have one graphics card in DOS / BIOS, but I was hoping that Windows + "driver magic" would maybe allow to switch to the second (inactive) card once it boots - similar to the way you can switch between displays if your card has two or more VGA outputs. Anyway, I am still going to buy two cards and will update this thread with my findings!
asdf53 wrote on 2022-04-02, 11:00:Thanks for your replies and the helpful insights, everyone. Sadly I do not have an AGP slot, it's an older Socket 7 board. I understand that you can only have one graphics card in DOS / BIOS, but I was hoping that Windows + "driver magic" would maybe allow to switch to the second (inactive) card once it boots - similar to the way you can switch between displays if your card has two or more VGA outputs. Anyway, I am still going to buy two cards and will update this thread with my findings!
I recently patched the HOT433 BIOS to properly work with Matrox G450 PCI cards. While the primary issue was related to PCI compatibility problems with the UMC8881 northbridge when PCI clock is only half the host clock, I learned a lot about the G450 PCI design: The G450 chip seems to be an AGP-type chip. The G450 PCI card includes a PCI-to-PCI bridge to adapt the G450 core chip to standard (5V compatible) PCI. This means that hardware support for switching to this card is very similar to "actual AGP cards". I don't know about software support, though. Thanks for keeping us updated.
