In the good old days, when you want to play with multiple OS, you have to have multiple computers. I still remember the time I have a Windows machine sitting next to a Linux box. Then a little bit later, multi-boot allows the same computer running different OS. I tried that too, but it ends up I stick with the primary OS most of the time, I　rarely boot into the secondary OS. Nowadays, running multiple OS in the same computer is much more convenient with virtual machine (VM). My host OS is Windows 7, and I can run 3 different OS simultaneously under each one’s own Window. It is kind of cool to have Windows 7 (a second copy), Linux (Ubuntu) and Mac OS X running on the same screen.

Virtual Box is a free software from Oracle, which inherited from Sun. It’s a type-2 hypervisor that relies on the host OS for low level functions. It is a bit slower than type-1 bare-metal hypervisor, but it has much better compatibity. I can use the USB and DVD-drive in the virtual machines and I can even create virtual LAN connections among those VMs. 3D graphics is probably the only draw back of type-2 hypervisor. Virtual Box works fine with 2D graphics, the VMs can play HD stream video without any lag. However, VM has limited 3D acceleration function, it has access to the graphics card on the host using DirectX9, good enough to play old games, but it not fast enough for latest games or Photoshop.

Another advantage of using VM is the saving snapshot of the virtual hard disk. Each VM has its own virtual hard drive and I can turn back in time simply by load up a saved snapshot. It is good to try out new or unknown software inside a VM first, so there won’t be any risk of virus or corrupting the Windows registry when uninstall the software. I always keep a copy of freshly installed Windows 7 virtual hard disk image and use it to try out anything new before installing on my host computer. It is also a neat trick to reset the trial period of some free software, especially those software that you only use once in a very long while.

Virtual Box is very easy to use, just follow the on-screen instruction. First you need create a new VM, allocate some memory and CPU cores to the VM, then create a new virtual hard disk, mount the OS installation disk, fire up the VM and install the OS as usual. If you are too lazy to install the OS, you can download pre-installed virtual hard disk image file from the web. My computer has 16GB of RAM, so I allocate maximum 4GB of RAM to each OS and I can have 4 VMs running at the same time without any problem. The OS running in the VM stays idle most of the time, unless you are doing some heavy number crunching tasks in more than 1 VM at the same time, you won’t even notice any performance hit to your host computer.

Virtual Box + Virtual Desktop works really well with each other. I usually put the VM in a virtual desktop and run it in full screen mode. It feels like the OS is running from a native installation instead running inside a VM.