IMGFS filesystem

May help

http//link.springer.com/article/10.1631%2FFITEE.1400133

"Windows Phone 7 is composed of two different file systems IMGFS and TexFAT. IMGFS is intended for system files and is compatible with Windows desktop file system. TexFATan ‘extended’ version of FAT that can handle files larger than 4GB."
Leaked document details Windows Phone 7 architecture
Windows Mobile 7

Here is another "random" google result
https://github.com/picoflamingo/imgfs

Though the question is unreferenced/vague, I guess that the OP might be interested in some tools related to the IMGFS used in Windows CE devices (and that should have not changed, or changed much, in later versions).

These, since they are Perl scripts, can be used (and abused) modifying them to suit the needs and extract filesystem format from them
http//forum.xda-developers.com/wiki/Hermes_HowtoExtractImgfs
More tools/scripts
https://itsme.home.xs4all.nl/

jaclaz