Modern monitors are capable of telling a video card (and software using the video card) details about it's capabilities, including which video modes it supports and details for operating parameters. The information from the monitor is called "EDID" (or Extended Display Identification Data). In some cases it's necessary to store this information as a file, so that EDID can be obtained from the file if the video card doesn't support EDID, if the monitor doesn't support EDID, or if the monitor's EDID provides incorrect information.
The EDID consist of one or more 128-byte blocks of data. The contents of any 128-byte block of data is defined by the Video Electronics Standards Association (http://www.vesa.org), and won't be covered in this specification.
Offset of the first 128-byte block of EDID from start of file
0x00000024
4 bytes
Number of 128-byte blocks of EDID present
Table 2.1 - Extended Header Format
Note: The "number of extended blocks" field at offset 0x7E in the first block (actually labelled as "Extension Flag" in the VESA specifications) should never be used. The "Number of 128-byte blocks of EDID present" field in the extended header is authoritative.