If you think about it, the Windows registry is the first and most deployed NoSQL database.
These databases are NoSQL as well. Albeit somewhat closer to traditional SQL than the registry: ESENT databases are made of B-trees, have column schema, primary/secondary indices, and support transactions. Unlike SQL servers, ESENT doesn’t have relations across tables, doesn’t have a query language (instead it has a low-level API to move cursors), and doesn’t support remote nor inter-process access, a DB is exclusive to a single process.
This is clearly false, how could you store user-specific data? (Hint: it's the NTUSER.DAT on each of the users' directory.) Additionally, you could create binary registry files and load them, funnily in much the same manner as how would mount drives on Unix and Unix-derived/inspired systems. Unless you consider that as a single root, the comparison that "Windows only has 1 registry" (which is wrong since that system-wide registry is backed up every boot and shutdown) is silly.
ESENT databases are independent: a database used by Windows search doesn't share anything with the DB used by windows update or Zune music.
Also, you've just ignored the whole line about loading custom registry files.
No idea. On Windows, I consider volume a single file system.
> you've just ignored the whole line about loading custom registry files
I know about them. If you really want multiple instances of the registry, you can also use virtual machines with guest Windows OS.
Still, 99% of Windows users don't do any of that. But their OS runs several programs like Windows search indexer which create and use ESENT databases. That's why I consider ESENT to be the most deployed NoSQL DB.
There are also magic aliases like HKEY_CURRENT_USER and (mostly system managed) links like CurrentControlSet.