BLG file format is used by Microsoft Windows Performance Monitor software application. This file format is used as a log file for windows performance.

The purpose of performance log file is to store various performance aspects of the windows so that this information can further be used for troubleshooting or for system optimization. The Performance Monitor application keeps a check on system performance and creates a binary log file with the available information. This allows the system to record its performance in the language which is understandable at machine level. Creating a binary log file also allows the system to use minimum space while creating a log file.