There are, as I understand it, two uses for RAM on a video card. One is the traditional use which is to hold the image sent to the screen. The other is to provide RAM for the GPU to do its calculations. The first takes a surprisingly
small amount of RAM. The original 16 colour VGA resolution needed only 154Kb to hold the image, and even full HD (1920x1080 32bit) only needs 8.1Mb. So if a mere 8.1Mb is enough to display full HD, why have 500Mb or 1Gb cards? The rest is used by the GPU crunching the numbers that create that 8.1Mb image, inclduing 2D and 3D acceleration, rendering and all the other tricks found on current cards. As I understand it the VBox graphics subsystem (at this time) is emulated and cannot make use of the hosts graphics card/GPU. Therefore everything that would normally be run on the GPU using video RAM has to be done by the host processor using system RAM. That is potentially going to take away a lot of processor time from the guest if the demands on the graphics are high and as a result could lead to poor overall performance. I also believe at this stage the emulated graphics subsystem is pretty basic. It can do 2D acceleration, but 3D acceleration (a necessity for most games) is only experimental. 2D acceleration can be accomplised easily in 128MB, and even 3D will work in that if the demands aren't huge, so 128Mb is plenty to make the graphics subsystem work, at least until 3D acceleration moves on from experimental to supported. No doubt the amount of video memory will be expanded in due course and 3D acceleration will become a standard feature, but that may only be possible if the host is 64bit and therefore can have lost of memory (over 4GB) installed. It is possible 32bit hosts simply wouldn't be able to cope with the demands of full on 3D acceleration in an emulated graphics card. And lets not forget, an ever increasing number of graphics cards are powered by highly parallel 128bit monster GPUs (64 or more cores isn't uncommon) that even a top end Corei7 can't match in terms of sheer number cruncing, so the chances of emulating a high end graphcs subsystem are pretty remote. I think it will only be when GPUs get the equivalent of VT-x/AMD-V that VBox can latch into and run video code directly on the GPU that VBox will be able to provide virtual high end graphics to the guest machines.
it's supposed to be a top notch virtual machine that runs today's high performance operating systems and their applications. That means games and Video editing and all sorts of things that actually need up to 1 gig or higher of video ram.
I've never seen that or anything similar written anywhere on the Vitualbox website. VBox was designed for server and workstation use to run server and business applications. All the other uses have sprung up since, but I don't believe it was ever intended that it should be used to run a modern high performance guest OS on top of a host to run very demanding applications, whether they are games, video editing or whatever. It actually makes no sense to run highly demanding applications on a guest under a host anyway. All guest OS's run more slowly inside a VM than they would straight on the host. This is partly because quite a lot of functions involve two layers of code. Hard disk writes for example are executed by the guest to the virtual drive, then again by the host to the physical drive. This all takes processor cycles to complete. Also the bits of the VM that have to be emulated, like the graphics, sound card, network card and so on use a lot of processor power to do the emulation. The nett result is a very noticable performance penalty. On my old PC I was able to run a direct comparison of Windows 98 as a guest under both VBox and MS VPC2007 on a WinXP host against it running 98 on the hardware. Even with all the tweaks enabled (including VT-x/AMD-V) the virtual machines were quite a bit slower, and bearing in mind Win98 flew on that PC to start with the slow down had to be significant to be noticable. I would say the VMs could have been running as slow as half the speed of the native install. What I am trying to say is running a game, video editing or other high end processor and hardware intensive software on a VM is like trying to run it on old harware - probably not a very good idea.