Why is the recommended memory on a VirtualBox guest OS 512MB?

I am preparing to create a virtual machine on VirtualBox. The wizard asks for the memory size to use for this guest machine and it is recommending 512MB. I have 16GB of memory on my computer so I would expect to be able to utilize more then just 512MB.

• Why does VirtualBox recommend 512MB?


• Is this a hard-coded value or is this a calculated value based on the amount of memory I have?


• What would be the ramifications of using a higher value, such as 4GB?

UPDATE:

I just read the following from the VirtualBox online documentation...

Depending on what guest operating systems you want to run, you will need at least 512 MB of RAM (but probably more, and the more the
better). Basically, you will need whatever your host operating system
needs to run comfortably, plus the amount that the guest operating
system needs. So, if you want to run Windows XP on Windows XP, you
probably won't enjoy the experience much with less than 1 GB of RAM.
If you want to try out Windows Vista in a guest, it will refuse to
install if it is given less than 512 MB RAM, so you'll need that for
the guest alone, plus the memory your operating system normally
needs.

So it sounds like they 512MB recommended is just a minimum and I will want to use as much memory as possible without taking up the memory my main computer will be using. But I would still be interested in learning your experiences with this issue.

Answer

The issue with odd initial values—like the setup wizard recommending 512MB for the guest OS—is a known quirk in VirtualBox’s setup wizard that is nicely explained in this article on the recent release of VirtualBox 5; bold emphasis is mine:

The GUI for creating a new VM is similar to previous versions, though
it provides odd default values. When creating a new Windows 7 64-bit
VM, the wizard recommended allocating 512 MB of RAM to the VM; the
minimum requirement for Windows 7 64-bit is 2 GB of RAM, making the
recommended value inadequate. The host system has 8 GB RAM, over half
of which was free at the time the wizard was started. The audience for
VirtualBox is IT professionals who would likely know better than to
attempt to use Windows 7 with that default value, so it is not a
particularly substantive issue.

Also, the official VirtualBox end user documentation addresses the odd minimum of 512MB of RAM recommendation; again bold emphasis is mine:

Depending on what guest operating systems you want to run, you will
need at least 512 MB of RAM (but probably more, and the more the
better). Basically, you will need whatever your host operating system
needs to run comfortably, plus the amount that the guest operating
system needs. So, if you want to run Windows XP on Windows XP, you
probably won't enjoy the experience much with less than 1 GB of RAM.
If you want to try out Windows Vista in a guest, it will refuse to
install if it is given less than 512 MB RAM, so you'll need that for
the guest alone, plus the memory your operating system normally needs.

Which is all to say, while VirtualBox has a “wizard” that slightly eases the setup/install process of a guest OS, it’s not designed to make every single decision—or assume decisions—you should make. VirtualBox is not a simple end-user piece of software like Word or Excel; it’s really a true power-user/admin tool.

There is a certain basic assumption of a user’s skills/knowledge that is connected to using virtualization software like VirtualBox. And ultimately at the core of that assumption is that someone using VirtualBox will know enough to make their own basic decisions when it comes to resource allocation when setting up a guest OS in VirtualBox.

For example, I can definitely use Ubuntu 12.04 (server) as a guest OS on my Mac OS X install of VirtualBox with 512MB of RAM. But it noticeably lags if I stress the server a bit. I prefer to keep it running with anywhere from 1GB to 4GB of RAM to make sure things run smoothly; depending on what I am doing/testing at the time.