Chkdskx and Formatx by Mark Russinovich

There used to be a time where, before they got purchased by Microsoft, Mark Russinovich's SysInternals provided a slew of very useful Windows utilities, with source. Of these, one of the most interesting had to be Chkdskx and Formatx, 2 utilities that leverage the fmifs.dll to duplicate as much as the Microsoft chkdsk and format functionality. Mark had the following to say about these utilities:

Have you ever wondered how exactly NT's two file system management utilities, chkdsk and format, work? Maybe you've had an application that would have been perfect if you could have incorporated chkdsk or format functionality into it. I present Chkdskx and Formatx, two utilities that very precisely clone the command-line chkdsk and format utilities that come with NT. In fact, the clones support the same switches as the standard chkdsk and format and produce almost exactly the same output. So while they don't do anything special, their source code demonstrates how you can write your own interfaces to chkdsk and format functionality.

The truth is, fmifs usage has barely changed since the days of Windows NT and what applied then to formatting and checking volumes still applies today if you want to format or check a volume in Windows 7 or Windows 8. Unfortunately however, the original SysInternals site went down around 2006, along with its utilities and source... Fortunately Mick's blog provided a link to a torrent of a full SysInternals site rip issued in 2006 (which I also duplicate here as well), and I will now make the original FMIFS.zip archive available here for your convenience, as it can be quite useful.

Or, if you want to have an overview of how fmifs.dll is used in a modern application, I can only invite you to have a look at the CheckDisk() and FormatExCallback()/FormatThread() calls of Rufus's format.c/format.h.