# Virtualbox Image



## bsd10 (Jun 11, 2010)

Does anyone know how Virtualbox creates its virtual disk? The documentation says it is just a file, but I would think it needs to be at least a vnode backed memory disk.


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## wblock@ (Jun 11, 2010)

The .vdi files are just files.  Sparse files, I suppose, since they aren't necessarily as large as the disk they represent.


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## bsd10 (Jun 12, 2010)

Do you know how this works? I thought you needed to boot off of a ram disk.


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## wblock@ (Jun 12, 2010)

Don't know what you mean.  VirtualBox gives the vm a preset amount of RAM out of the host's memory.  The hard drive image can be an actual hard drive, a fixed-size file, or a variable-size vdi file that only tracks blocks that have been written.


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## bsd10 (Jun 12, 2010)

I've always seen operating systems boot with a ram disk, but I never really knew why. After reading this, it seems like a legacy thing to support small boot media or low amounts of ram. I guess these restrictions don't affect Virtualbox.


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