Compact 34.8 KB RAR archive named after the HEF4556B, a dual 1-of-4 decoder/demultiplexer from the 4000-series CMOS logic family. The archive most likely holds the component datasheet with pinout, truth table, electrical limits and package drawings. A technician uses it to confirm pin functions while probing the chip on a board, check supply voltage ranges and identify a suitable replacement part. Compare the marking and package on the actual chip with the datasheet variants before swapping, since suffixes indicate different packages.
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 @IT_SERVICE_WORLD. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.