Manual:Protection

Protection is used to restrict the making of changes to a page (edit or move), the creation of a page, or the upload of a file.

MediaWiki handles existing and not-existing pages differently, because not-existing pages don't have a page ID.

That's why protection information is stored in two different tables, and listing of such pages are separate.

Database
Information about protected pages or titles is stored in the  and  tables.

Special pages
A list of protected pages can be found at Special:ProtectedPages.

A list of protected titles can be found at Special:ProtectedTitles.

API
A page can be protected with the  API.

A list of protected pages can be retrieved with the  API, using the   parameter.

A list of protected titles can be retrieved with the  API.

Hooks
occurs whenever the software receives a request to protect an article occurs after the protect article request has been processed