Unity 4.0 Overview
Oneiric Ocelot heralds the second incarnation of the Unity GUI in the desktop edition of Ubuntu, but it's actually version 4.0. Version 3.0 shipped with last April's Natty Narwhal, version 2.0 was included in the Netbook Edition of Ubuntu 10.10 Maverick Meerkat, and version 1.0 appeared in Ubuntu Light, the OEM-only instant-on companion OS.
While no functionality was lost between Natty's version of Unity and now, several features shifted to other areas of the UI. The three main elements of Unity are the Panel, Launcher, and Dash. This trinity make up the bones of Ubuntu's Unity GUI. The image below is a desktop map of Ubuntu 11.10.
The Unity Panel takes up two dozen pixels at the top of the screen. This Panel is akin to the upper panel from the GNOME 2 desktop, which was the default GUI in versions of Ubuntu before Natty Narwhal, along with countless other Linux distributions. This is where the System Tray is housed and Notifications appear.
The Unity Launcher is the taskbar/dock that takes up the left side of the screen. To make the Windows analogy, the Launcher houses Start menu, the window list, and Quick Launch functionality.
Dash is essentially the Ubuntu Start menu. It houses shortcuts to everything from applications to operating system utilities to files and folders.
Each of these three elements and the features that comprise them are detailed on the next three pages.