CHKDSK is a utility within Microsoft Windows operating systems (Win2k onwards) designed to check for file system and hard disk errors with the ultimate aim of preserving the life of a hard disk drive.
Chkdsk evolved from a utility called Scandisk, the only difference being that ChkDsk supports NTFS volumes whereas Scandisk was FAT only. Its primary aim is to find and repair corrupt or damaged file system data, it also has the ability if manually selected to do so, to check for hard disk integrity issues such as bad sectors.
Some of the most common reasons why ChkDsk will run are power loss, application and OS crashes and incorrect shutdown. When most of these situations occur, the computer will most likely be processing critical data!
In brief, ChkDsk does not prioritise user data! That which is of most importance to you! The primary aim of ChkDsk is to preserve the integrity of the file system. As a result, you will find files with the extension .chk in folders with names similar to 'FOUND.000'. Chances are if you have ever had ChkDsk run on your Windows PC/server/hard disk you will have these folders on your drive.
When one of the above triggers ChkDsk to run what happens in the background is as much data as is possible is read from the area noted as being ‘bad’ and moved to a .chk file within one of the folders such as FOUND.000. This is done with no regard to what that data was; its file extension, file name and any other meta data is completely ignored. One specific reason that ChkDsk runs is when a hard disk develops bad sectors, something all disks will do during their normal operation. However, modern hard disks have the ability to remap bad sectors to unused areas of the disk during normal operation. If the disk has gotten to a stage whereby a disk utility needs to be run it is highly likely that the disk has reached a stage where complete drive failure is imminent.
TRC Data Recovery have released a new software application called ChkBack which is designed to retrieve data that has been lost after ChkDsk has scanned a drive and relocated file fragments. You can find a copy of ChkBack here:3 Years, 8 Months, 3 Weeks, 3 Hours, 32 Minutes ago.