How much memory (RAM) should I allocate to the Virtual Machine?

You should give virtual machine however much RAM you need for the tasks you're using it to perform.

If you're running a single virtual machine, the suggestion you read is OK (provided that your host machine has enough RAM, which it does). However, depending on what you plan to do with your Ubuntu system, it probably doesn't need 2.7 GB of RAM. I give most of my virtual machines, including Ubuntu virtual machines, 1 GB of RAM, even when I have enough physical RAM available that I could allocate more.

If you plan to run multiple virtual machines, then giving a virtual machine 2.7 GB of RAM out of a total of 6 GB is probably too much. It would not work out well to have two VM's with that amount of RAM!

Finally, your virtual machine will typically reserve all the RAM you give it, whenever it is running. When the virtual machine is turned off, suspended, hibernated, or otherwise not running, this RAM will not be in use. For example, I have about 10 virtual machines, most of which have 1 GB of RAM, on a host machine with 4 GB of RAM. This is not a problem; it just means I can only run up to a few of them at a time.

There is not a fixed rule on the amount of RAM we assign for exclusive use by a virtual machine. However there are two points we need to take care of:

• assign enough RAM for the guest OS to run smoothly (> 512 MB for 64-bit Ubuntu)
• leave enough RAM for the host OS including host applications (> 2 GB for 64-bit Windows 7)

Virtual Box Manager will warn you whenever you assign more than 50% of RAM to a virtual machine, but in case we have plenty of RAM this is a rule of thumb recommendation only. Of course we can assign more than 50% of the system RAM to our VM as long as we have enough RAM left for our host OS.

Note that we don't have to worry too much about the amount of RAM we assign to a newly created machine as we can easily change this at any time later.