difference in performance: virtualbox os and local os

Question

Is there a specific difference in performance between an OS installed on a Virtual Box and an OS installed locally on a computer?

Is there any formula so that I could know what is lost when you install an OS in a virtual box.

For example, if you assigned 512Mb of memory in a virtual box os. But it is actually 256Mb when compared to its performance when it is installed locally.

Please, I need the information because we're making a comparative analysis on operating systems. And I can't just install Sabayon Linux, it might ruin the 3 other os that I have already installed.

Answer 1

Given the number of variables involved (everything from caching efficiency to what programs are running your host OS) it is practically impossible to know the exact difference theoretically. However, I would do the following to determine this experimentally without affecting my current install;

Overview:

1. Purchase an identical harddrive to what you currently have installed in your computer.
2. Remove the current harddrive you have so you don't mess up any of your currently installed stuff.
3. Install the OS's that you are analyzing to that harddrive -- note, they MUST not be installed in different partitions and the drive should be zero'd between changing the operating systems (this more closely simulates how it might look under virtual box -- i.e. a fresh drive).
4. Perform your benchmarking for each OS
5. Put your old harddrive back in
6. Fire up VirtualBox and install each OS, perform your benchmarking for each OS.

Caveats:

• If you are trying to do a high-quality comparative analysis, you HAVE to do the comparison from each individual OS ON the hardware.
• Make sure you pick a good set of benchmarking software that doesn't bias toward one thing or another to heavily. And if you do bias toward something heavily (RAM usage perhaps?) make sure you get enough samples that the aggregate data is meaningful.
• Ensure the software running on your host os is the same AND minimal during your benchmarking process for each OS you sample
• I would recommend defragging your harddrive between installs of the OS's under virtualbox, this will help ensure the virtual disk will be more contiguous on disk

Answer 2

There is, actually, a specific difference.

In a virtual machine, the hardware that the OS thinks it's running on is not real.

Whereas in a local, bare-metal OS, the hardware that the OS thinks it's running is, by and large, actually physically present.