Windows Vista has some great additions. One of them is the new and re-designed Performance Monitor. You can open the Performance snap-in from the Computer Management tool (see below), or as a separate snap-in.

Inside the Performance tool you will find a Monitoring Tools folder, and in it you will find the Reliability Monitor. The Reliability Monitor is a snap-in for Microsoft Management Console (MMC) that provides a system stability overview and details about events that impact reliability. It calculates the Stability Index shown in the System Stability Chart over the lifetime of the system.

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Microsoft, Windows Vista, Reliability Monitor, Tips, Knowledgebase