Chk-Back

Chkdsk is a well-known, rather old yet still useful utility that lists and fixes disk errors. During file system recovery operations, this utility saves the contents of lost or cross-linked clusters to CHK files.

Therefore, though they often contain only junk data, CHK files may still contain data useful for file recovery purposes, such as entire lost files of various types and formats. Unfortunately, a tool capable of scanning the CHK files, showing you their contents, and helping you recover the files that they contain, is not offered by Microsoft, so you have to resort to third-party tools. There aren't many of those neither; CHK-Mate, UnCHK, and Chk-Back are the most popular of them, and Chk-Back is also my personal favorite. That's mostly because Chk-Back is really simple, small, and straightforward, and it also never disappointed me.

It's impressively precise and reliable thanks to the fact that it detects the files contained by a CHK using a powerful and accurate signature-based comparison algorithm. It compares the start of the file potentially contained by the CHK, known as the header, to the headers from an internal database of known file types. This also shortens the scanning and detection time, as it eliminates the need of using a hexadecimal editor or trial and error to detect and recover the needed files.

Chk-Back is very simple and convenient to use even for beginners. Its only additional options are the possibility to select the location of the CHK files and the capability of filtering the potentially found files by their types and formats (for example, you can choose to search only for videos, or only for AVI, MPG, MP4, or other video file formats).

Chk-Back is not only lightweight, fast, easy-to-use and reliable, but also free. In my opinion, if you ever need to deal with CHK files in order to recover lost files, this handy little tool is worth a shot.