Updating the ide drive
For the inquisitive Virtual Box user, this section describes in more detail how they work.
A differencing image is a special disk image that only holds the differences to another image.
As opposed to a physical disk however, Virtual Box allows you to expand an image file after creation, even if it has data already; see Section8.23, “VBox Manage modifymedium” for details.
Irrespective of the disk capacity and format, as briefly mentioned in Section1.7, “Creating your first virtual machine”, there are two options of how to create a disk image: fixed-size or dynamically allocated.
In general, you should avoid IDE unless it is the only controller supported by your guest.
This applies to all of the aforementioned image formats (VDI, VMDK, VHD or HDD) and irrespective of whether an image is fixed-size or dynamically allocated. To mark an existing image with one of the non-standard modes listed below, use To illustrate the differences between the various types with respect to snapshots: Assume you have installed your guest operating system in your VM, and you have taken a snapshot.As a result, the differencing images can form a complex tree with parents, "siblings" and children, depending on how complex your machine configuration is.Write operations always go to the one "active" differencing image that is attached to the machine, and for read operations, Virtual Box may need to look up all the parents in the chain until the sector in question is found.The variety of controllers is only supplied for Virtual Box for compatibility with existing hardware and other hypervisors.Disk image files reside on the host system and are seen by the guest systems as hard disks of a certain geometry.