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I don't know if here is the best place to ask, but:

Do anyone know how can i use the Video memory of an offboard PCI video card as an extent to the main memory on windows XP?

Is there any modified kernel or any way to modify it in order to do that?

I have an i486 DX4 running with 24Mb, and a offboard PCI video card with 16Mb of memory, and it usually have more than 10MB free, so, how could i use that memory from the video card to enhance my main memory?

Thanks.

> 486 > WinXP
You are joking, aren't you? WinXP requires Pentium MMX to run (unless you've rebuilt the kernel and a lot of libraries from WRK source (removing fast assembly routines for memcpy and memset) and removed everything that uses RDTSC).
Yes, using video RAM as expander is possible (here's guide for linux: https://wiki.archlinux.org/index.php/swap_on_video_ram , `mtd' kernel module is required, you can find similar module for Win32 but i'm not sure that you can force video driver to use only part of available VideoRAM) but it's very slow (especially reading from it) + AFAIK, you can configure this memory region only as uncached or write-combined, i.e. fast write-back caching is not available.

i486 DX4 is a rather nice CPU but one should use OS that is optimized for it.

But it is an optimized Win XP, i installed microXP and removed everything i could from it, drivers, services, the explorer, files that are not needed and registry entries.

The result was a 250Mb Win XP that only takes a total of 24Mb of memory (including everything, kernel memory, drivers and essential processes), and this counting with the video card driver that i'm using now, which is pretty heavier than the one i'll use on the i486, so i think it'll take 19Mb only, but i need some Mb free if want to run something on it else than an image visualizer, paint, calculator or notepad.
Also, i don't now about the memory intake oscilations during the windows startup.

you may do not want to run xp without 128 mbyte of ram. also, an 586-class cpu required to run windows xp. for such tiny configs, you should run windows nt or 98se instead