On dumb monitors, the EDID information is on a tiny flash chip. My previous employer accidentally shipped a monitor where we (actually our CM, which we failed to catch) failed to disable writes, so the computer could actually overwrite it. Fortunately, this rarely happens, but we did get some reports of it happening - possibly due to a dodgy connection (you shouldn't treat data flowing over any unpluggable cable as 100% reliable, including the 'this is a read' bit ).