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.