"Any operating system has several different levels that make up the software stack. As an example, let's look at Ubuntu. At the bottom, you have the kernel. The kernel deals with interaction with the processor, switching between tasks and input/output (filesystem, keyboard input etc). In Ubuntu, this is the Linux kernel. On top of this, you have the basic libraries that provide APIs (Application Programming Interfaces) that allow you to do common tasks in a standard way without dealing with the underlying kernel. On Ubuntu, this is the GNU C Library. From there, you can write and run applications. Typically, the most useful one is something for a user to interact with. In the olden days it used to be a shell (like the DOS shell or bash). These days people are used to having a graphical interface, so you have another service that abstractly deals with graphics. On Ubuntu is this it the X.org Server. On top of that is built a user interface, which on Ubuntu is GNOME."

"When you write an application, although you generally have access to all levels from the kernel upwards, but generally you try and use the highest level that is useful as they abstract away the complexity - although you don't have to. Now for Android, imagine that everything from the APIs upwards has been completely replaced with something completely different, and on top of that they've built extra layers that only provide certain secure ways of accessing the layers below. So although it's 'Linux' as it uses the Linux kernel, it looks and feels completely different to both the user and the programmer. In fact, you could actually remove the Linux kernel and replace it with one that acts similarly and you wouldn't be able to tell the difference - the only reason Linux kernel is used is because it's free, available for many platforms and is quite advanced."

Google Desktop Linux, not Linux Desktop