Extended Display Identification Data

Extended Display Identification Data and Enhanced EDID are metadata formats for display devices to describe their capabilities to a video source. The data format is defined by a standard published by the Video Electronics Standards Association.
The EDID data structure includes manufacturer name and serial number, product type, phosphor or filter type, timings supported by the display, display size, luminance data and pixel mapping data.
DisplayID is a VESA standard targeted to replace EDID and E-EDID extensions with a uniform format suited for both PC monitor and consumer electronics devices.

Background

EDID structure versions range from v1.0 to v1.4; all these define upwards-compatible 128-byte structures. Version 2.0 defined a new 256-byte structure but it has been deprecated and replaced by E-EDID which supports multiple extension blocks. HDMI versions 1.0–1.3c use E-EDID v1.3.
Before Display Data Channel 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.
This problem is solved by EDID and DDC, as it enables the display to send information to the graphics card it is connected to. The transmission of EDID information usually uses the Display Data Channel protocol, specifically DDC2B, which is based on I²C-bus. The data is transmitted via the cable connecting the display and the graphics card; VGA, DVI, DisplayPort and HDMI are supported.
The EDID is often stored in the monitor in the firmware chip called serial EEPROM and is accessible via the I²C-bus at address. 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 the X.Org Server 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.
E-EDID was introduced at the same time as E-DDC, which supports multiple extensions blocks and deprecated EDID version 2.0 structure. Data fields for preferred timing, range limits, and monitor name are required in E-EDID. E-EDID also adds support for the Dual GTF curve concept and partially changed the encoding of aspect ratio within the standard timings.
With the use of extensions, E-EDID structure can be extended up to 32 KiB, because the E-DDC added the capability to address multiple 256 byte segments.

EDID Extensions assigned by VESA

Timing Extension
Additional Timing Data Block
Video Timing Block Extension
EDID 2.0 Extension
Display Information Extension
Localized String Extension
Microdisplay Interface Extension
Display ID Extension
Display Transfer Characteristics Data Block
Block Map
Display Device Data Block : contains information such as subpixel layout
Extension defined by monitor manufacturer : According to LS-EXT, actual contents varies from manufacturer. However, the value is later used by DDDB.
Revision history
August 1994, DDC standard version 1 – introduce EDID v1.0.
April 1996, EDID standard version 2 – introduce EDID v1.1.
November 1997, EDID standard version 3 – introduce EDID v1.2 and EDID v2.0.
September 1999, E-EDID Standard Release A – introduce EDID v1.3 and E-EDID v1.0, which supports multiple extensions blocks.
February 2000, E-EDID Standard Release A - introduce E-EDID v1.3, based on EDID v1.3. EDID v2.0 deprecated.
September 2006, E-EDID Standard Release A – introduce E-EDID v1.4, based on EDID v1.4.
Limitations

Some graphics card drivers have historically coped poorly with the EDID, using only its standard timing descriptors rather than its Detailed Timing Descriptors. Even in cases where the DTDs were read, the drivers are/were still often limited by the standard timing descriptor limitation that the horizontal/vertical resolutions must be evenly divisible by 8. This means that many graphics cards cannot express the native resolutions of the most common widescreen flat-panel displays and liquid-crystal display TVs. The number of vertical pixels is calculated from the horizontal resolution and the selected aspect ratio. To be fully expressible, the size of widescreen display must thus be a multiple of 16×9 pixels. For 1366×768 pixel Wide XGA panels the nearest resolution expressible in the EDID standard timing descriptor syntax is 1360×765 pixels, typically leading to 3-pixel-thin black bars. Specifying 1368 pixels as the screen width would yield an unnatural screen height of 769.5 pixels.
Many Wide XGA panels do not advertise their native resolution in the standard timing descriptors, instead offering only a resolution of 1280×768. Some panels advertise a resolution only slightly smaller than the native, such as 1360×765. For these panels to be able to show a pixel perfect image, the EDID data must be ignored by the display driver or the driver must correctly interpret the DTD and be able to resolve resolutions whose size is not divisible by 8. Special programs are available to override the standard timing descriptors from EDID data. Even this is not always possible, as some vendors' graphics drivers require specific registry hacks to implement custom resolutions, which can make it very difficult to use the screen's native resolution.

EDID 1.4 data format

Structure, version 1.4

Detailed Timing Descriptor

When used for another descriptor, the pixel clock and some other bytes are set to 0:

Monitor Descriptors

Bytes	Description
0–1	= Monitor Descriptor.
2	= reserved
3	Descriptor type. `FA`–`FF` currently defined. `00`–`0F` reserved for vendors.
4	= reserved, except for Display Range Limits Descriptor.
5–17	Defined by descriptor type. If text, code page 437 text, terminated with LF and padded with SP.

Currently defined descriptor types are:

: Monitor serial number
: Unspecified text
: Monitor range limits. 6- or 13-byte binary descriptor.
: Monitor name, for example "PHL 223V5".
: Additional white point data. 2× 5-byte descriptors, padded with 0A 20 20.
: Additional standard timing identifiers. 6× 2-byte descriptors, padded with 0A.
: Display Color Management.
: CVT 3-Byte Timing Codes.
: Additional standard timing 3.
: Dummy identifier.
: Manufacturer reserved descriptors.
Display Range Limits

Descriptor

With GTF secondary curve

With CVT support

Additional white point descriptor

Color management data descriptor

Bytes	Description
0–4
5	Version: `03`
6	Red a₃ lsb
7	Red a₃ msb
8	Red a₂ lsb
9	Red a₂ msb
10	Green a₃ lsb
11	Green a₃ msb
12	Green a₂ lsb
13	Green a₂ msb
14	Blue a₃ lsb
15	Blue a₃ msb
16	Blue a₂ lsb
17	Blue a₂ msb

CVT 3-byte timing codes descriptor

Additional standard timings

CTA EDID Timing Extension Block

The CTA EDID Extension was first introduced in EIA/CEA-861.

CTA-861 Standard

The ANSI/CTA-861 industry standard, which according to CTA is now their "Most Popular Standard", has since been updated several times, most notably with the 861-B revision, 861-D, 861-E in March 2008, 861-F, which was published on June 4, 2013, 861-H in December 2020, and, most recently, 861-I, which was published in February 2023. Coinciding with the publication of CEA-861-F in 2013, Brian Markwalter, senior vice president, research and standards, stated: "The new edition includes a number of noteworthy enhancements, including support for several new Ultra HD and widescreen video formats and additional colorimetry schemes.”
Version CTA-861-G, originally published in November 2016, was made available for free in November 2017, along with updated versions -E and -F, after some necessary changes due to a trademark complaint. All CTA standards are free to everyone since May 2018.
The most recent full version is CTA-861-I, published in February 2023, available for free after registration. It combines the previous version, CTA-861-H, from January 2021 with an amendment, CTA-861.6, published in February 2022 and includes a new formula to calculate Video Timing Formats, OVT. Other changes include a new annex to elaborate on the audio speaker room configuration system that was introduced with the 861.2 amendment, and some general clarifications and formatting cleanup.
An amendment to CTA-861-I, CTA-861.7, was published in June 2024. It contains updates to CTA 3D Audio, and clarifications on Content Type Indication, and on 4:2:0 support for VTDBs and VFDBs. It also introduces a new Product ID Data Block, to replace the Manufacturer PNP ID in the first block of the EDID, since the UEFI is phasing out assigning new PNP IDs.