Search notes:

ucrtbase.dll

In Visual Studio 2015, the CRT was split into two parts
ucrtbase.dll contains the UCRT and ships as operating system component with and since Windows 10.
The source code for the UCRT is installed along with Visual Studio, by default under C:\Program Files\Windows Kits\10\Include\sdk-version\ucrt. The sdk-version corresponds to a version (for example 10.0.1.14393.0 for the Anniversary update).
The corresponding (architecture dependent) *.lib are under C:\Program Files\Windows Kits\10\bin\architecture\ucrt (with, for example, x64 for architecture).
The redistributable (that is: non-debug) DLLs itself are under C:\Program Files\Windows Kits\10\Redist\ucrt\DLLs\architecture.

Misc

The UCRT is the Windows equivalent of Linux's glibc.

See also

The source code for the UCRT is stored in the %UniversalCRTSdkDir%\Source\%UCRTVersion% directory.
The include files to use the UCRT are in %UniversalCRTSdkDir%\Include\%UCRTVersion%
Compare with the ucrtbase_dll that is found in an Office installation.

Index