The Dallas Semiconductor DS1287 Real-time clock (RTC) integrated circuit (IC), which houses a non-replaceable lithium battery requiring careful destruction of the housing to replace.
This particular chip wasn't soldered to the board, but socketed on the CPU board of the Schneider Tower AT System 220 from 1988.
<a href="//commons.wikimedia.org/wiki/User:MarcoTangerino" title="User:MarcoTangerino">MarcoTangerino</a>
<span class="int-own-work" lang="en">Own work</span>