Computer monitors can also easily display the output of a program in a user friendly manner. For example, one would have to be intimately knowledgeable about a specific early computer and its display system, consisting of an array of lights, to even begin to make sense of the status of the computer's hardware. In contrast, anybody who can read should be able to understand a well-designed user interface on a modern system, without having to know anything about the hardware of the computer on which the program is being run.