Resmon.exe is the Windows Resource Monitor, a powerful tool to observe processes and the system: CPU, network, memory and drive usage. It is installed on every Windows system since Vista. Start it by typing resmon or by button click in the Task Manager.

More:

• https://technet.microsoft.com/en-us/library/dd883276%28WS.10%29.aspx
• https://blogs.technet.microsoft.com/askperf/2012/02/01/using-resource-monitor-to-troubleshoot-windows-performance-issues-part-1/
• http://www.digitalcitizen.life/how-use-resource-monitor-windows-7