A. Xperf in an advanced performance monitoring tool that helps create logs with detailed performance information about an OS, including boot information. You view the logs using the xperfview tool.
These tools are documented on this site. To use them, you need to download the Windows Software Development Kit (SDK), which is available here, and select the Install Now option. The initial download is small because it's just a downloader for the rest of the SDK (which is very large). However, if you only want Xperf, unselect everything except Windows Performance Toolkit (you have to keep part of .NET Development) to cut it down to around 200MB instead of a couple of gigabytes.
Once it's installed, a folder will be available at C:\Program Files\Microsoft Windows Performance Toolkit that contains the xperf toolkit.