Graphical user interface
Because of their versatility, operating systems based on the Linux kernel can be also found in mobile devices that are actually touchscreen-based embedded devices, such as smartphones and tablets, together with personal digital assistants (PDAs) and portable media players that also include a touchscreen. This is a challenge for most learners because their computer experience is mainly based on GUI (Graphical user interface) based interaction with the machine and high-level programming on the one hand and low-level programming of small microcontrollers on the other hand while the concept of command line interfaces is widely unknown.