It can't run over ~1.5 GB (2 Gigs technically) in Windows anyway because it's only 32-bit. Ubuntu is also a very heavy Linux operating system with lots of overhead. If you tried something like Elementary, Arch, or Linux Mint in the VM i'm sure it would run faster (Linux Mint also has enhanced support for running inside VirtualBox). I have Linux Mint on my laptop, and it runs just fine (even on an old Intel 945GM). I haven't tried in VirtualBox though, but I will soon. @historic_bruno: just out of curiosity, what host and guest OS are you using (and what VM software?)