Windows 10: Games Can't utlize full VRAM

Hi! Yesterday I noted while playing GTA 4 that even though MS store shows i have 1 GB VRAM but GTA 4 shows i have 507 MB. Please let me know the way to utlize full vram. According to device manager i have Intel HD graphics 5500

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Anti-aliasing in games and its relation with VRAM

I know the fact that Anti-aliasing is a very heavy process in games and slows down the game play even on strong hardware but I want to understand it more in order to make the best choice in graphic settings in games.

I've read here How much VRAM do you really need at 1080p, 1440p and 4K? that games like GTA V can take up to 4GB of VRAM on 1080p resolution. but turning on the AA option increases the amount, maybe up to 5GB VRAM. I have AMD Radeon R9 390X with 8GB VRAM. I've tested it with this game and watched the VRAM usage using monitoring programs like Afterburner but none of them could still answer my question.

is AA something to depend mostly on the available VRAM and not the GPU cores? the games uses half the VRAM, (I can turn on frame scaling and let the game even use all 8GB of VRAM), I wanna know if I turn on AA will it only use the free VRAM or it will put extra load on the GPU too and as a result slow down the game and lower overal FPS? thanks!
I'm using latest AMD Radeon driver and Windows 10 X64

 

Increase VRAM

My laptop comes with 128mgb of VRAM, which means it cant support most games that need more vram. I upgraded it to 512 VRAM using the regedit technique: is there any way to make it higher than that?

 

Windows 10 reserved VRAM

My in game graphics settings indicate that Windows has reserved 532 MB of VRAM that is now inaccessible to the game. Since it's a primarily gaming computer I'd like to maximize the amount of available VRAM for the game. Does Windows really need .5 GB of
VRAM to do very very little in the background, and is there any way to change how this operates? It's very annoying considering I bought a less powerful GPU on the assumption that I'd be able to utilize all of it?