Brendan wrote:Note that there's "system RAM" and "video RAM"; and the video mode itself will use 0 bytes of "system RAM" (and will only use "video RAM"). The system RAM is used by code that generates data to put into the frame buffer (in "video RAM"); and this varies significantly depending on how you do it.
Uhm, despite what most people think, discrete VRAM is the exception, not the rule - the overwhelming majority of desktop and laptop systems use CPU integrated graphics, and set aside part of the system RAM for the IGPU/APU to use.
Intel has had integrated graphics on the majority of their consumer and enthusiast CPUs for over ten years. I am not sure if any of these IGPUs can work with a separate video memory bus, but AFAIK none of them require one.
AMD sells separate product lines with and without integrated GPUs, calling the models with the 'Advanced Processing Units' (APUs). They generally don't produce APU versions of their enthusiast and high-performance lines. The latest APUs, the Ryzen 3 2200g and the Ryzen 5 2400g, just came out last month, and are still getting through their teething pains (mostly relating to motherboards which need to be updated before they will work with the integrated graphics).
As it happens, I was just trying to learn about these this past week, in preparation of a new desktop system sometime in the coming year (I hope; I probably shouldn't be spending the retroactive payment I will be getting - hopefully in the tomorrow or Wednesday - but I think I can legitimately argue to myself it on mental health grounds). I am figuring if I can be certain that the motherboard will be an updated one - which should be possible by, say, early May, which is when I mean to do this if I can - which would give me a rather modern system for, I dunno, $800 US or so (including a monitor) if I am careful.
(BTW, Brendan, you might want to take a look at the TechYesCity YT channel and website on this, as he discusses the hardware market - including low-price builds - in Australia, and usually gives both USD and AUD prices he's found.)
However, the OP's question is relating to a type of system that one is unlikely to find outside of a museum today - the
486DX2 was a model which Intel sold briefly in 1992 to buy breathing space to get all the bugs (well, except
the FDIV bug 
) out of the original Pentium. While I have seen 20 year old PC systems still in regular use today, I don't think I have seen a
25 year old one that anyone other than a vintage hardware enthusiast was using regularly.
Sit down, I have a bit of a history lesson for all of you.
Now, in the
PS/2 Video Graphics Array and the ISA/EISA cards meant to copy it, the video memory was dedicated... sort of. VGA used the 64KiB set aside in the original 5150 PC memory map (from 1981, which keep in mind was designed to support
four text-mode video pages using an
MDA, or two graphics pages on a
CGA, neither of which exceeded 16KiB - they had the foresight to expect that this would need to be extended later, which obviously EGA and VGA did, as did things like Hercules, Tandy, and MCGA graphics), whose highest resolution modes was 640x480, 4-bit (16 colors), and highest color mode was 320x200, 8-bit (256 colors).
By late 1990, when 80486DX mobos and CPUs started to come out in notable numbers, VGA was pretty much the baseline, and early
SVGA (original 800x600, 4-bit) were pretty common, with SVGA2 (1024x768, 8-bit) cards being the high-end cards (less for gaming than for AutoCAD, as most PC games only supported up to VGA, and often supported multiple older video models). When running in real mode, these continued to use the existing 64 KiB mapped memory space by bank-switching the video memory slot; generally, this was done in the card's implementation of VBE.
However, by 1992, as
SXGA (1280x1024, 8-bit on a 5:4 aspect ratio, or 1280x960, 8-bit when retaining the 4:3 aspect ratio) started to really get traction, more games were using 32-bit extenders to run bigger games, and would need to either stick to the defined VGA registers and hope the card makers were diligent, or bundle drivers for several cards.
A few years later still - 1995-97 - it became common for a game developer to issue separate versions of their existing games, optimized for one or more of the video cards which were current in vogue (which at the time usually mean either S3 or 3Dfx), but by then, no one who was running those cards would have put them in a motherboard running a DX2 (even if the could find a motherboard which socketed 486 but had a PCI slot instead of a VLBus one).
Of course, by the time of Windows 98, you had releases of both DirectX and OpenGL for Windows which were no longer quite so terrible as those in 1995-97, which made it relatively easy to write 3D graphics software for Windows PC without having to write your own modified drivers (though it would be a while still before games using either of them were particularly common). By then the 486DX2 was... well, actually, a lot offices still had them, really, usually running windows 3.1, but they were already getting phased out even by dead-broke NPOs like the one in worked for in 1999.