A sitemap index needs to be in the website root, but do the referenced sub-sitemaps also need to be in the root?

All we need is an easy explanation of the problem, so here it is.

My Website have to split on three Sections , Windows 10, Windows 8 and Windows 7 .Now build Three articles which explain how install Virtual Box on Windows 10, Windows 8 and Windows 7 , therefore build a sitemap for every sections;

<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"
        xmlns:news="http://www.google.com/schemas/sitemap-news/0.9">
<url>
 <loc>http://htmlkurss.xyz/windows10.php</loc>
 <news:news>
   <news:publication>
    <news:name>htmlkurss</news:name>
    <news:language>de</news:language>
   </news:publication>
   <news:genres/>
   <news:publication_date>2019-03-28</news:publication_date>
   <news:title>Wie instaliert Virtual Box in Windows 10 </news:title>
   <news:keywords>Virtual Box, installation, Windows 10</news:keywords>
  </news:news>
 </url>
</urlset>

Name File , sitemap_windows10.xml . Then for Windows 8 and Windows 7. My Idea is to build a sitemap structure as here say .

When the sitemaps_index.xml should to be on Root of the site, where should to be the Sitemaps referenced (sitemap_windows10.xml)?

How to solve :

I know you bored from this bug, So we are here to help you! Take a deep breath and look at the explanation of your problem. We have many solutions to this problem, But we recommend you to use the first method because it is tested & true method that will 100% work for you.

Method 1

Stephen Ostermiller give me the solution .I have a few mistake to do….

Because my Website is not a News Site (Newspaper) , I can’t to write <news:news> .
How now to write my sitemap .

<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"
    xmlns:news="http://www.google.com/schemas/sitemap-news/0.9">
    <url><loc>http://htmlkurss.xyz/windows10.php</loc></url>
</urlset>

and every time which write a new article , add the link to these File .The File stay on Root of the site .Without to write a sitemap index .

Note: Use and implement method 1 because this method fully tested our system.
Thank you 🙂