EDID stands for Extended Display Information Data. This is the data contained (usually in a small EEPROM) on each DVI display or HDMI sink. There may be as many as one EDID per DVI or HDMI input.
The source device checks the display’s DVI or HDMI port for the presence of an EDID prom and uses the information inside to optimize the output video and/or audio format. The EDID data structure can be for either VESA PC devices or for CEA-861B E-EDID (Enhanced EDID) devices. All sink devices compliant to the DVI or HDMI specification must implement EDID.
An EDID PROM is used only in sink devices. An EDID PROM sits on the DDC channel and uses a 2-wire I2C bus (part of the DDC specification from www.vesa.org) to communicate from the sink to the source. The EDID PROM contains information about the sink that it resides in. Its job is to communicate the preferred (or supported) video and audio formats and resolutions to the originating source. As an example, when a DVD player is powered on, it reads the EDID from an attached HDTV. The HDTV will have in its EDID contents that it is a Samsung 17” LCD panel that supports native resolution of 1280x1024 pixels, but can also support 480p, 720p and 1080i video modes. The EDID may also say that the TV is an HDMI device and has 2-speakers. The DVD player would compare this information with what it can put out of its HDMI port, then set itself to send 1080i with 2-channel stereo to the HDTV.