http://en.wikipedia.org/wiki/Extended_d ... ation_dataExtended display identification data (EDID) is a data structure provided by a computer display to describe its capabilities to a graphics card. It is what enables a modern personal computer to know what kind of monitor is connected. EDID is defined by a standard published by the Video Electronics Standards Association (VESA). The EDID includes manufacturer name, product type, phosphor or filter type, timings supported by the display, display size, luminance data and (for digital displays only) pixel mapping data.
This command causes the PC to query the display to it can setup the correct output resolution. A very important function that allows you to connect your PC to anything and have it adjust itself otherwise you would have to preset the output for the particular display application using your current monitor to do so... how would your PC know to switch to the other profile for the other monitor?