Windows Memory Diagnostic is a built-in tool in the Windows operating system designed to test your computer's RAM for errors. It helps identify issues that may cause system crashes, slow performance, or unexpected behavior. The tool runs a series of tests to check the memory's integrity and can be accessed by typing "Windows Memory Diagnostic" in the search bar. To use the tool, you can choose to restart your computer immediately or schedule the test for the next boot. Once the test is complete, Windows Memory Diagnostic will display the results, helping you determine if your RAM needs replacement or further investigation.