How does a 32-bit OS handle more than 4 GiB of video RAM (VRAM)?

From what I understand, the maximum available RAM on a 32-bit OS is 4 GiB (not GB) minus VRAM (video RAM), so with 1 GiB of VRAM, the system can use up to 3 GiB RAM, regardless how how much larger the RAM is.

But what if you give it more than 4 GiB of VRAM? Will it just fail to boot? Or will it split into 2 GiB RAM, 2 GiB VRAM or something like that?

(Note: GiB are powers of two, GB are powers of ten.)

the video ram is used by the gpu, can be some part of the main ram, but in some cases it has its own dedicated ram (which is not available/visible by the cpu)

Memory mapping is all "smoke and mirrors". Maybe you should look all the way back to PAE in this context.

Originally Posted by exerceo From what I understand, the maximum available RAM on a 32-bit OS is 4 GiB (not GB) minus VRAM (video RAM)

No!

VRAM is handled by GPU exclusively. Therefore it has nothing to do with the 32-bit = 4 GiB address space limit of a 32-bit OS. A little bit more complicate is a system with a chipset or processor IGP that uses "shared memory" (a portion of installed RAM).

If CPU doesn't provide PAE (physical addrerss extension) or mainboard doesn't provide "memory remapping", 4 GiB minus address spaces of mainboard components and add-in cards are available for addressing main memory (RAM). A common limit is 3,25 GiB for addressing RAM.
If CPU provides PAE and mainboard provides "memory remapping", 64 GiB minus address spaces of mainboard components and add-in cards are available for addressing RAM.

In reality, the 4 GiB limit can be reached with late ia32 mainboards (e.g. socket-478, socket-775, socket-A) or with x86_64 mainboards, and the 64 GiB limit can be reached with newer x86_64 mainboards.

On ia32 mainboards with AGP slot and without "memory remapping" support, another limit occurs if an Ati AGP graphics card is used: If more than 2,75 GiB RAM is installed the system is useless because it doesn't work stable. Start of address range of Ati AGP graphics cards is fixed at 2,75 GiB. This collides with installed RAM > 2,75 GiB (commonly 3 GiB or 4 GiB) that cannot be remapped due to missing "memory remapping" support from mainboard.
A solution in this case ist reducing installed RAM to commonly 2,5 GiB (3 slots: 1 GiB + 1 GiB + 512 MiB; 4 slots: 1 GiB + 1 GiB + 256 MiB + 256 MiB).
Another solution is replacing the Ati AGP graphics card with a nvidia AGP graphics card to enable full use of installed 3 GiB RAM or use of about 3,25 GiB of 4 GiB installed RAM, but Linux & nvidia graphics cards is something like matter & antimatter …

Originally Posted by exerceo From what I understand, the maximum available RAM on a 32-bit OS is 4 GiB (not GB) minus VRAM (video RAM), so with 1 GiB of VRAM, the system can use up to 3 GiB RAM, regardless how how much larger the RAM is. But what if you give it more than 4 GiB of VRAM? Will it just fail to boot? Or will it split into 2 GiB RAM, 2 GiB VRAM or something like that?

The BIOS wouldn't let you give it that much. The only time you assign system memory to a gpu is if its an integrated GPU (either on cpu like modern chips or on motherboards like back in the 32-bit days), and the system isn't gunna let you assign too much. Usually its 1G or less. A discrete GPU (video card) has its own VRAM, and not used by the OS...

Originally Posted by exerceo From what I understand, the maximum available RAM on a 32-bit OS is 4 GiB (not GB) minus VRAM (video RAM), so with 1 GiB of VRAM, the system can use up to 3 GiB RAM, regardless how how much larger the RAM is.

Yeah.... that's not correct.

I actually have no real clue about this, but I would guess it would be like MIDI instrument banks.
Midi can only do program (instrument) changes from 0-127, aka, an 8 bit value.
So there's "banks" to increase that limit, then you have 128 banks each with 128 instruments.

So I would guess that a 32 bit system can handle a lot more ram by just dividing it into chunks that have 4gig boundaries, or something, divided into banks, which would be tracked by the system.

Again, though, this is pure speculation and I'm not even looking it up to see if I'm right or wrong. Lol.
It's just such a 'direct' solution to that problem that I'd be surprised if it weren't the thing that's being done.

Originally Posted by clueless_dolt So I would guess that a 32 bit system can handle a lot more ram by just dividing it into chunks that have 4gig boundaries, or something, divided into banks, which would be tracked by the system.

The CPU cannot address more RAM (than 4G) at a time, but obviously you can switch on/off those banks to use different ones.
see for example here: https://www.golinuxhub.com/2014/02/u...-pae-in-linux/ (post #3)

Yeah, that's why even with PAE and a system with 8G, a single app still has the 4G limit on 32-bit system.