BLG files are so-called Windows Binary Performance Log Files, which are binary log files that are created during the performance monitoring of a Windows system with the Windows System Monitor. Blg files include data on resource utilization and performance, such as memory (RAM) usage, hard disk and CPU used by various programs over a period of time.
BLG files are mainly used to analyze server and computer load to detect possible problems.
BLG files use a proprietary format, which can be converted to csv format with the command line relog. In addition, not all Windows versions use the same BLG format. Blg files can also be viewed with the performance monitoring of Windows. With Start -> Control Panel -> System and Security -> Administration -> Power Monitoring -> Power Monitoring (left) you get to the current power display. In the window to be opened with 'ctrl + L' you can find a log file in the tab 'Source'.