how to kludge a 486 PC into thinking it has a video card?

From: Jim Leonard <>
Date: Mon Feb 21 10:35:33 2005

On Mon, Feb 21, 2005 at 11:26:33AM -0500, Steve Thatcher wrote:
> in order for you to fool the bios you will need some hardware that will
> "respond" to key areas that the bios is interested in.
> Picking a mono card as a target, you will need hardware that allows for
> writes and reads of memory from b000:0 to b000:7fff (the end address may be
> a lower location). I don't think the bios does a real memory test, so you
> may be able to use one register that lets the cpu write a value to it that
> can be read back (the register should respond to all addresses in the range.

This is an assumption; I know for a fact that different BIOS
manufacturers check in different ways; for example, Award vs.
Phoenix vs. AMI. Some write to registers; some write to video RAM;
some do both; some do neither (read $3d8 for verticle retrace
status or other methods).

The only universal/compatible way to fool the BIOS into thinking a
card is in the machine is to *put a card in the machine*.
Jim Leonard        Email:
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Received on Mon Feb 21 2005 - 10:35:33 GMT

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