Original Apple, fully tested version 1 ROM low for the Macintosh Plus. This is one of two 128K ROM chips on the Macintosh Plus logic board. There were two versions of this ROM identified by the last character of the Apple part number on the chip i.e. 342-0342-A or 342-0342-B.
NOTE : The v1 ROM low must only be used alongside either the v1 or v2 ROM high (342-0341-A or 342-0341-B).