That feature is called differential download packages, which is a technical term for "only downloads what you need." A differential download looks at the files already on your system and uses them to rebuild the new OS version from there. It sounds simple, but as Microsoft's Laura Butler points out, it's no easy task given the decades of legacy code and patches. For a major release like the Creators Update, you'll still need to download a full build, but the next feature update after that should be significantly smaller -- about 35 percent smaller on average, according to Microsoft's Director of Program Management Bill Karagounis. For Windows Insiders those downloads should be even smaller, but it's a bit of a trade-off since those systems get hit with more frequent updates.