There is only one file type that uses the .LOG1 extension:
Windows Registry Hive Log File
Log file used by the Windows registry; contains a trace of changes that have been made to the user's registry over time; typically found in the user's directory or under the %SystemRoot%\System32\config directory in Windows; saved in a binary format and as a hidden file in Windows.
LOG1 files are a part of the overall group of files that comprise the registry "hive." Other files include .LOG and .LOG2. A common LOG1 file is ntuser.dat.LOG1.
|Microsoft Windows Registry||Included|
Updated: March 11, 2010