FWIW, I run multiple virtual machines (Windows 8, 7, and XP, Ubuntu, and more) on my 2012 MacBook Air 13". I'd run out of space fast using the internal SSD, so

FWIW, I run multiple virtual machines (Windows 8, 7, and XP, Ubuntu, and more) on my 2012 MacBook Air 13". I'd run out of space fast using the internal SSD, so instead I have a USB 3 external HD that I run the virtual machines from. Now, I'm usually only running one virtual machine at a time, but really, it runs very nicely, far faster than I would have expected.