Oracle database 12c: The Multithreaded Database
A 12c new feature that may have significant performance and scalability implications is the multithreaded database. All releases of Oracle below 12.x (and 12.x by default) run on Unix in a multi process model. The various background processes (typically at least fifty for 12c, thirty or forty for 11g) run as separate operating system processes. Furthermore, the dedicated server processes that support sessions also run as separate operating system processes. An Oracle instance will usually be running as hundreds (perhaps thousands) of processes. The multithreaded database changes this.
12 MArch 2013 update: Content removed - it exceeded what is permitted for the pre-release status of the product.
Sorry about that, will repost when I can.