Files with the .REGTRANS-MS extension contain data that co-creates a Windows transaction diary – namely transaction data regarding the reading or saving of changes in the user and system registry recovery data, which is stored in NTUSER.DAT or SCHEMA.DAT files.

REGTRANS-MS files are created by a Windows operating system component for creating transaction logs called Microsoft CLFS, which stands for Component Log File System, and are stored in Users and WindowsSystem32SMIStoreMachine folders on the system disc – usually marked with the letter C.