Some older operating systems used a database-filesystem or database like filesystem as storage.
I heard older IBM systems had something like this. BeOS had BeFS with inbuilt metadata index. NTFS + WinFS in user land vision was a bit like this. Office server aka MS Sharepoint (which implemented WinFS vision for intranet) stores all files in the database.
> I heard older IBM systems had something like this.
Most (non-Unix) mainframe and minicomputer operating systems β not just IBM's β have support for record-oriented files and indexed files in the filesystem. The functionality is roughly equivalent to that of non-relational "flat file" databases or key value stores. Examples include ISAM and VSAM under z/OS (aka MVS), and RMS under OpenVMS. This is in contrast to Unix and Windows, where the filesystem itself only supports files as unstructured bytestreams, and any record structure or index structure is imposed by higher levels such as applications or shared libraries.
You might also be thinking of the IBM minicomputer operating system OS/400 (nowadays called "IBM i"), which embeds a relational database (a variant of DB2) into the operating system. (I have often wondered how deep the integration actually isβI believe it is something deeper than just bundling a relational database with an OS, like how many Linux distributions include MySQL or Postgres, but I don't really know.)
I heard older IBM systems had something like this. BeOS had BeFS with inbuilt metadata index. NTFS + WinFS in user land vision was a bit like this. Office server aka MS Sharepoint (which implemented WinFS vision for intranet) stores all files in the database.