virtualbox.org

Hey, I've noticed with Virtualbox that it does not allow more than 128MB or 256MB of video memory in guest OSes. Unfortunately some apps/games that require 3D acceleration need more than that, I know that this feature is most likely highly requested, but will we ever have the option to allow more than 256MB of Video memory in Virtualbox, like hyper-v & vmware do?
Sadly I cannot use hyper-v due to apps not working with it enabled and I can't use VMware because it has severe audio problems, so VirtualBox is kind of my only option.

Like you said, this has been asked for a lot. We here on the forum can't control what the devs do or why they have decided to limit to 128/256MB. You can put an enhancement request on the Bugtracker.

It's basically a character limit on the number that's used to keep track of how much video memory the virtual machine is simulating. Like the amount of video memory can't be expressed as a number larger than 2^32-1, or something. Anything larger than that causes a rollover error. And this decision was made so long ago, and is buried so deep in the code, that it can't be changed without breaking over 9,000 other things, or so the developers want us to believe.

I'm more worried about the lack of Direct3D support AT ALL in WinXP machines going forward.

No, the main reason for the limit IMV is that more would just be RAM wasted to no benefit. Virtual graphics RAM is simulated using normal host PC RAM, so it's not actually any faster than buffering graphics in a normal RAM buffer - which is what apps will do anyway if they run out of special "vram".

IME around 10 times the frame size is plenty RAM for buffering.

Bear in mind that the OpenGL renderer is actually on the host. That's where VRAM is needed, not sitting doing nothing in a VM.