These files are version 3.11 (1990) of the Adaptec AHA-1542B SCSI BIOS.

They need to be written to 27C128 EEPROM chips or thier equivalent.

File 1542BU12V311.BIN Goes in socketed position U12 (The MCODE chip)

File 1542BU13V311.BIN Goes in socketed position U13 (The BIOS chip)