
At a minimum, give Ubuntu at 1GB (1024MB) of RAM. The drawback is that OS X will have less to use while Ubuntu is running.

The more memory you give to Ubuntu, the faster it will run. As illustrated in the screenshot below, my total RAM is 4GB, so I allocated half of it to Ubuntu, and the other half to OS X. Now you’re going to decide how much memory (RAM) you’re going to allocate to Ubuntu when it’s running, and how much to leave for OS X.Make sure the Type: is set to Linux and the Version: is Ubuntu (64 bit). Give your “ virtual machine” a name (something descriptive is good, but it doesn’t matter).

When VirtualBox opens, click the New button.

Following is the step-by-step guide for you to install Ubuntu on VirtualBox on Mac OSX:
