Boardview for the Apple iMac A1419 logic board 820-01134, revision A as given in the name. Apple uses the 820-xxxxx pattern for its main boards, and the suffix letter marks the revision. The .brd layout opens in tools such as OpenBoardView, FlexBV or Boardviewer, letting you search part designators, follow nets between components and find test points while chasing a short or missing power rail. Match the 820 number silkscreened on the board before trusting pin locations.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @boardviews. Enginerys does not host this file.
How to open a .brd file
The most common boardview extension. Several unrelated formats share it, which is why one viewer opens a .brd and another refuses it.