"BIOS Compatible" likely means that the card only supports high-level functions that the official VGA BIOS made available to the machine via Int 10h. Anything that directly accesses the video card's registers and/or exploit non standard video modes will crash and burn. For that you need a "register compatible" card like the rest of the industry developed.

Performance will be horrible when the card does work since using Int 10h is slow compared to programming the hardware directly. This is even worse in protected mode as the application has to switch to real mode to access Int 10h services. Its likely there were "native" drivers later developed that supported the C&T chip's registers. Microsoft's tech note hints to that.

Are there any DOS games that use BIOS-mode only?

NJRoadfan wrote:

"BIOS Compatible" likely means that the card only supports high-level functions that the official VGA BIOS made available to the machine via Int 10h. Anything that directly accesses the video card's registers and/or exploit non standard video modes will crash and burn. For that you need a "register compatible" card like the rest of the industry developed.

Performance will be horrible when the card does work since using Int 10h is slow compared to programming the hardware directly. This is even worse in protected mode as the application has to switch to real mode to access Int 10h services. Its likely there were "native" drivers later developed that supported the C&T chip's registers. Microsoft's tech note hints to that.

Well. There is a good chance it will still work by writing directly to video memory. I am betting only things like mode sets and palette changes
would require 0x10 which isn't THAT bad. Well hopefully it is atleast register compatible enough for plane changes in 640x480x16 mode