As part of reshuffling things, cutting down on old features and introducing new features that happen with any new software release, Microsoft decided to bring the axe down on a relatively useless feature called Windows Experience Index on Windows 8.1. Windows Experience Index or WEI is a benchmarking tool that rates the performance of a computer based on its hardware and software configuration. However, the tool was not entirely removed, and it was still possible to generate the WEI scores by running a process via the command prompt. It was only a matter of time before someone came up with a proper frontend to the process that benchmarks the system. The time has come.
ChrisPC Win Experience Index is a free program that runs the benchmarking tool, reads the scores generated by the program and displays it in a window that resembles the original Windows Experience Index interface.
The benchmarking process too works just as it did with the original tool. Close any other running applications, launch ChrisPC Win Experience Index, and click "Rate this computer". The program will then carry out its various tests while you wait. Once it’s finished, you’ll see separate scores for your CPU, RAM, graphics and hard drive, with the lowest highlighted as the "base score".
ChrisPC Win Experience Index works not only on Windows 8 but on Windows 7 and Windows Vista as well.
Edit: Another tool that brings back the missing Windows Experience Index tool is Winaero WEI Tool