In the present specification, various embodiments are disclosed of digital devices and methods of processing data in said digital devices. Here, a digital device according to an embodiment of the present invention comprises: a user interface unit for receiving execution requests for a first application through to a fourth application; a decoder for decoding data on the applications for which the execution requests were made; a control unit; and an output unit for outputting first through to third display windows and application data in each of the display windows. The control unit controls the execution of the first application; divides a screen according to the second application execution request; implements controlling to generate a first display window and a second display window for the divided screen and output the first application data and the second application data in the first display window and the second display window, respectively; implements controlling to output the third application data in the second display window in which the second application data is being output, when the third application execution request is received; and implements controlling to further divide the screen, generate a third display window for the further divided screen, and output the fourth application data in the third display window, when the fourth application execution request is received and the fourth application data is related to the third application data.