Most people like that use Perforce (e.g., Google).
And no, they don't split into multiple repos, they might well have the entire company's source code in a single repository (code sharing is way easier this way).
That's a pretty terrible way to share code. Simple example: I work on a project, write some code. Turns out that code is useful for someone else, so they reach in and include it, which is easy since it's all the same repo and all delivered to the build system. Now I make a change and break some customer I didn't even know exists. Oops.
And no, they don't split into multiple repos, they might well have the entire company's source code in a single repository (code sharing is way easier this way).