A path name without space is often required when installing many programs. Since the default installation path in the English version of Windows is "C:\Program files\", these programs which require that the path name contains no space, often choose "C:\" as their installation path.
If you don't want to install them directly under "C:\", you could create a folder called for example "Program1" or "Program_files" on the C partition. Windows won't like it though if you create a folder called "Program" directly under "C:\".