You were busy working on your computer, opened a few files here and there. Then the next thing you knew, you accidentally saved over the file you were working on. And the last thing you can remember was that you clicked on something. Nothing else. Doesn't this scenario sound familiar to you?
Don't you worry. You're not alone in experiencing this kind of trouble. In fact, modification and accidental file deletion is the most common cause of losing data. It's a good thing that Windows Vista has found a way to address this problem through its “Shadow Copy” feature.
What is Shadow Copy feature
The Shadow Copy feature automatically makes a point-in-time copies of files as you are working on them. With those copies, you can easily get versions of a document before you have accidentally deleted or replaced it. Thus, Shadow Copy solves the following issues.
1)Accidental deletion of files
2)Accidental replacement of files
3)Corruption of Files
In short, gone files are retrieved and recovered with Shadow Copy.
How Shadow Copy Works
Two methods are used to make Shadow Copy work. One is by making a clone or full copy and another one is by copy-on-write.
Clone (Full Copy or Split Mirror). Just like what its name implies, this method creates a full copy of the original file or data. Through hardware or software mirroring, this is made possible. What happens is the original file or volume take the changes while the shadow copy file or volume becomes and remains as read-only copy of the original at certain points of time.
Copy-on-Write. Unlike the clone method that creates full copies of the original file, the copy-on-write works by making differential copies. What happens is that this method makes a copy of the original version before new changes overwrites it.
What are the Components Used in Creating Shadow Copies
In creating shadow copies, these three components are important: providers, writers and requestors.
Providers are software responsible for creating shadow copies by managing data or volumes and creating shadow copies of them as demanded. Meanwhile, writers are software that are responsible in not letting data inconsistencies to happen. They respond to signals and provides information such as application name, files to exclude or include. And on the other hand, requestors are a backup application that initiates the creation of Shadow Copy.
How to Retrieve files with Shadow Copy
Accessing this feature is as easy as 1-2-3. You just have to right-click on the folder of file and select “Restore previous versions”. With that, Windows XP will let you go back in a previous time and lets you access the folders and files' versions corresponding to the previous dates. Files will be hierarchically arranged. And so as not to give you a headache in deciding which file is which, you can preview each file as read only. This way you would be able to determine which file to retrieve or restore. And to make sure that you have fully restored a file, simply drag the file to a folder. Or, you can select the file and click the Restore button so it'll return to its original location.
Shadow Copy Service of Window Vista 
