Before the advent of Reliability Monitor, Windows users had few ways in which to accurately determine how well their PCs were performing. Essentially, you would install the OS, a hardware device, or software application, or perhaps you would update the driver for an existing device. Any one of these actions could cause the PC to work better or, in the more memorable experiences, cause it to swoon wildly out of control, perhaps blue-screening down to a hard stop. In such cases, you would have to rely on your own memory to figure out what happened: Was it the RAM I just installed? Or perhaps that Adobe software update? Sometimes you'd simply never know.
Windows Vista builds on the troubleshooting tools provided in previous Windows versions to help you figure out what's going on with your PC. There are older tools like Performance Monitor, Event Viewer, and the Disk Defragmenter that have been improved somewhat in Vista. And then there are tools that are brand new to Vista. Reliability Monitor is the most useful of those new tools.
Because Microsoft considers the Reliability Monitor to be an advanced diagnostic tool--which I think is ridiculous, by the way--it is hidden away in the Reliability and Performance Monitor management console. You can access this console, which includes the updated version of the Performance Monitor in addition to the new Reliability Monitor and a cool Resource Overview view, in a variety of ways. There are a variety of ways to launch this tool, but the simplest is to type "relia" (no quotes) in Vista's Start Menu search box and clicking the link that appears for Reliability and Performance Monitor.
The Resource View is displayed by default, and it provides a nice is overly simple overview of your CPU utilization, disk activity, network activity, and memory utilization in real-time graph form, along with expandable detail views of each.
Secret: The CPU utilization chart is nice, but it's not as detailed as the one you get in Task Manager. For example, Task Manager displays separate CPU usage graphs for each physical CPU, CPU core, or even CPU Hyper-Threading (HT) unit; the Resource View shows a single graph only.
To access Reliability Monitor, click on the Reliability Monitor link under Monitoring Tools in the left pane. The view will change to display a line chart detailing your system's reliability over a period of time from the day you installed Vista through today. Reliability Monitor provides an overall score, or System Stability Index, which measures your system's reliability as of this moment on a scale from 0 to 10. You can also look back over time and see the trends that caused the System Stability Index to go up or down. If you experience an application failure, for example, the score will go down on the day that failure occurred. Meanwhile, the score can rise after successive days with no issues.
Reliability Monitor tracks five kinds of issues: Software uninstalls, application failures, hardware failures, Windows failures, and the vaguely-named miscellaneous failures. To find out what's going on with your system, you can click any column in the line chart and the System Stability Report section at the bottom will expand appropriately to show what, if anything, happened on that day. There are different icon types displayed in the chart that detail the types of issues that happened. A red "x" is the most serious: This represents an application crash, OS stoppage, or other major issue. A yellow "!" triangle (or "bang") represents less serious issues, such as non-responding applications. A white "I" (or information) balloon represents the least serious issues: You'll see this for software uninstalls or other issues that don't necessarily affect your score but are notable nonetheless. For days in which there are no icons, nothing happened: Either you didn't use the PC at all or everything went smoothly.
Tip: If you want the System Stability Report to display every single issue that's occurred on your PC since you installed Windows Vista, click the drop-down list box in the upper-right corner of the window and choose "Select All."
Reliability Monitor is important because it helps you pinpoint what's going wrong on your PC. If you are experiencing bizarre crashes, this tool can help you determine if it's a hardware-related issue or a software problem. If a particular application is crashing repeatedly, you can see that and decide whether you want to uninstall it. You can also use Reliability Monitor in tandem with Vista's Problem Reports and Solutions control panel to alert Microsoft of problem devices and software: Vista does this automatically, but you can manually launch this tool by running Control Panel and navigating to System and Maintenance and then Problem Reports and Solutions. Then, click on Check for new solutions to trigger an upload of your problems to Microsoft. Any failure that has triggered a Reliability Monitor issue will be sent to Microsoft and, when solved, you'll be alerted via a pop-up. You can also view your problem history to see a list of issues you've submitted.
Tip: Administrators and power users can run Reliability Monitor against remote computers on the local network. However, you will have to configure this capability on the PC that you'd like to access remotely by enabling the Remote Registry service to run automatically.
Secret: You may be curious how Vista creates the score for the System Stability Index. Microsoft tells me that recent failures are weighted more heavily than past failures, while periods of success are rewarded with the assumption that older issues have been resolved. Days in which the PC is powered off are not included in the score.
source: Paul Thurrott