Next, we need to create a virtual hard disk and virtual box will allow you to select a few different formats to use.
In the new virtual disk wizard you can choose any of the following:
1) VDI: Virtual Box has its own drive format which gives good performance but not readable by other hypervisors (YET).
2) VMDK: This is the default VMware format used by both VSphere and workstation. If you have workstation installed you can mount the file as a drive on the host operating system.
3) VHD: The default standard used by Microsoft with Hyper-v and can be mounted directly from Windows 7 and Windows 8 as well as Server 2008 r2 and Server 2012. Can also be mounted to a Xen hypervisor such as Xenserver.
4) HDD: This is the default format used by Parallels workstation for both Windows and OS X.