MTTD is the average time (mean) it takes to discover that a hardware or software component has failed. MTTD is a critical part of the Mean Time To Repair (see MTTR entry) calculation. Early detection of failures, or warning of impending failures, is vital. MTTD can be reduced for IT systems by performing proactive Application Performance Management (APM), Network Performance Management (NPM), and system monitoring with tools such as KEMP 360.