Apple Macbook Air is a pretty amazing notebook, but there are still plenty of folks out there that understate its capabilities. This also include people that want to virtualization on their computer and thus go in for something like Macbook Pro or other notebook. However, these people do not realize that the current generation Macbook Air pack enough power to run virtual machines butter smooth, and in some cases, better than Macbook Pro (thanks to SSD).
For Virtualization, VMware is a good choice. I have personally found the VMware to be more stable than the Parallels even though latter runs a bit faster. I, however, prefer stability (of VMware) over speed as I do not like things crashing down when I am doing something crucial. Keep in mind that when you are using VMware, the storage will shrink (or grow) according to the space needed. This is great as most of us get the middle range model of Macbook Air that comes with 128GB SSD.
I virtualize Windows 7 on my Macbook Air 2011 (Core i5, 4GB RAM, 128GB SSD) to run Mathcad, LTSpice, PCSpim, Microsoft Office and Firefox web browser. So yes, even with 4GB RAM, I have yet to experience any sort of slowdown. Go ahead and do all the virtualization you want on your Macbook Air. It is a perfect computer for doing almost any computer task, unless you are into heavy gaming.
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