Display is the user interface that is used to show useful information. Displays can be as cheapest as LEDs and as expensive as LCD panels. Depending upon the requirements and costs a variety of displays is avaialble. CRT dispalys are most common in industrial applications. LEDs and LCDs are suitable for embedded systems. The information can be displayed in number of ways depending upon what type of display you are using. An LED can be used just for indication signals like LED when on system is working. Dot Matrix based on LEDs is a cheaper way to display text. But programming becomes much complex with Dot Matrix. LCD and Plasma screens come in number of variety and are quite expensive. LCD crystal displays are less expensive and quite useful than LEDs or dot matrix.