Windows 7 does not natively include drivers for the USB 3.0 eXtensible Host Controller. This often caused issues during installation on modern hardware (like Intel's Skylake platform), where USB keyboards and mice would stop working during the setup process. The utility solved this by "injecting" the necessary drivers into the boot.wim and install.wim files of the installation media. How to Achieve the Same Result Now
Conclusion
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