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When a PC boots, it typically goes through the POST/BIOS phase where it prints things like "detecting drives" or "press any key to boot from CD" and "press F1 to edit BIOS options."

I have multiple video cards in one system (it's used for GPU computation, so there are not displays hooked up to all the cards.. some don't even HAVE a display output).

My problem is that different PCs seem to have different rules about where and if the POST screens are displayed. I may have only one display hooked up to one of 3 installed video cards, but the PC doesn't seem to find that display. This means I can't edit BIOS options or select among multi-boot OS options.

Once I boot an OS (linux or windows) there's no problem.. it's the pre-OS and bootloader phase where machines simply don't display.

What's the "rule" for display adapters during POST? Especially if there's more than one video card installed. The common sense logic of "if you have only one display hooked up, use that one" does not seem to be true.

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I would expect that what the BIOS detects as the video and what you are thinking about are two different things. The BIOS is a very small program with limited abilities. Most likely the BIOS is looking for a device that supports VGA interrupt calls and finding one, it uses it.

If I understand your situation correctly, the BIOS is using one of the cards you don't have a monitor hooked to. Once the OS boots, it can load all kinds of drivers and interact with all your hardware and monitors.

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I agree, you could try moving the cards around to see if the BIOS will find the card if it is in a different slot. –  einstiien Feb 15 '10 at 2:35
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