EDID structure versions range from v1.0 to v1.4; all these define upwards-compatible 128-byte structures. EDID structure v2.0 defined a new 256-byte structure, but subsequently has been deprecated and replaced by v1.3 which support multiple exension blocks. HDMI versions 1.0–1.3c use EDID structure v1.3.
Before Display Data Channel (DDC) and EDID were defined, there was no standard way for a graphics card to know what kind of display device it was connected to. Some VGA connectors in personal computers provided a basic form of identification by connecting one, two or three pins to ground, but this coding was not standardized.
The channel for transmitting the EDID from the display to the graphics card is usually the I²C-bus, defined in DDC2B (DDC1 used a different serial format which never gained popularity).
The EDID is often stored in the monitor in a memory device called a serial PROM (programmable read-only memory) or EEPROM (electrically erasable PROM) and is accessible via the I²C-bus at address 0xA0. The EDID PROM can often be read by the host PC even if the display itself is turned off.
Many software packages can read and display the EDID information, such as read-edid for Linux and DOS, PowerStrip for Microsoft Windows and XFree86 for Linux and BSD unix. Mac OS X natively reads EDID information and programs such as SwitchResX or DisplayConfigX can display the information as well as use it to define custom resolutions.
Enhanced EDID was introduced at the same time as E-DDC; it introduced EDID structure version 1.3 which supports multiple extensions blocks and deprecated EDID version 2.0 structure (although it can be supported as an extension). Data fields for preferred timing, range limits, and monitor name are required in E-EDID. E-EDID also supports dual GTF timings and aspect ratio change.
With the use of extensions, E-EDID string can be lengthened up to 32 KBytes.
EDID Extensions assigned by VESA
- Timing Extension (00h)
- Additional Timing Data Block (CEA EDID Timing Extension) (02h)
- Video Timing Block Extension (VTB-EXT) (10h)
- EDID 2.0 Extension (20h)
- Display Information Extension (DI-EXT) (40h)
- Localized String Extension (LS-EXT) (50h)
- Microdisplay Interface Extension (MI-EXT) (60h)
- Display Transfer Characteristics Data Block (DTCDB) (A7h, AFh, BFh)
- Block Map (F0h)
- Display Device Data Block (DDDB) (FFh)
- Extension defined by monitor manufacturer (FFh): According to LS-EXT, actual contents varies from manufacturer. However, the value is later used by DDDB.