Instant Recovery and Snapshot Software
Instant Recovery / Snapshot software is a related technology whose approach is quite different to that of Light Virtualization. Their main advantage is that they allow users to accumulate changes to the system across several reboots. These changes can be saved as new snapshots at any time, and any of these snapshots can be restored in mere seconds and when needed. This enables users to go backwards and forwards in the time-line of their systems, switching between saved snapshots at will.
With snapshot software users can safely test a new driver, a Windows update or any other program that requires a reboot. You just install anything you want, and then reboot to see if it is useful and suitable to your needs. If it has caused problems, or if you decide you don't want to keep it for some other reason, then there is no need to uninstall it. Just restore an older snapshot that was taken before the program in question was installed. Upon rebooting, all changes that have happened in the meantime will be completely undone and the protected disk/partition will be reverted back to the exact state it was when you took the snapshot you are restoring. This is an invaluable function for testing new software.
The way this works may vary considerably between different programs of this kind. In this instance I will be outlining the basic principles behind the fastest variant of this technology, the true Instant Recovery/Snapshot software (as opposed to other software who also use the term 'snapshot', but whose functions are similar to those of traditional backup programs). During installation the snapshot software will ask you to select which disk/partition it should protect. You must always choose your system disk/partition, it is the one that holds your Windows installation and is normally designated as the C: drive. Once installation completes, the program will restart your system, and will take a snapshot of the protected disk/partition before Windows loads. This is often called a baseline snapshot, the common base on which all future snapshots will be branching out from.
The snapshot software also adds a boot sector driver to the system. This driver enables users to press a key upon system start-up and before Windows starts loading, and access the snapshot software's pre-boot interface. From there users can take a new snapshot, restore an existing one, and also defragment or delete previously created snapshots.
One of the greatest benefits of this technology is the fact that when you save or restore a snapshot, no actual data transfer takes place (as opposed to traditional backup methods where data is being copied over to a different location when backing up/restoring). The inactive snapshots are still there on the same disk, saved on sectors that Windows and every other software deem as empty space; so there is no data transfer and no waiting time when creating or restoring a snapshot - it all happens in a few seconds. Windows and all other programs can only see the snapshot that you have chosen to boot from. The snapshot software keeps a sector map which enables it to see what data is common to one or more snapshots. This way there is no data replication among snapshots, every new snapshot will only include the disk sectors that have been changed since its parent snapshot was taken.
After Windows has loaded, the snapshot program utilizes a driver which protects those inactive snapshots from being overwritten by the OS. This driver intercepts all writes addressed to sectors that contain inactive snapshot data, and redirects such writes to truly empty sectors. This is seamless; there is no noticeable overhead even on older and less powerful systems. Of course the more changes that have taken place since the parent snapshot was taken, the more disk space a new snapshot will occupy. Loading huge snapshots still takes mere seconds though, all thanks to the fact that the data is still there on the same disk.
The following image is a visual representation of the way snapshots work. Of course the specific links between the snapshots in the picture are for indicative purposes only. Users can actually return to any snapshot at any time, add or remove new software or make any other changes to the system, then save the new setup as a new snapshot.