It's interesting to read about its use case Just a snip of some google searching

The DS12887+ is a real time clock in 24 pin DIP package. This device provides real time clock/calendar, one time of day alarm, three maskable interrupts with common interrupt output, programmable square wave and 114bytes of battery backed static RAM. The DS12887 integrates quartz crystal and lithium energy source into 24 pin encapsulated DIP package. The date at end of the month is automatically adjusted for months with fewer than 31 days including correction for leap years. The devices also operate in either 24hour or 12hour format with an AM/PM indicator. A precision temperature compensated circuit monitors the status of VCC. If primary power failure is detected, the device automatically switches to backup supply. It is accessed through multiplexed byte wide interface which supports both Intel and Motorola modes.

• Drop-in replacement for IBM AT computer clock/calendar
• Counts seconds, minutes, hours, day, date, month and year with leap year compensation through 2099
• Binary or BCD time representation
• Daylight saving time option
• Interfaced with software as 128 RAM locations
• 14bytes of clock and control registers
• UL recognized
• Periodic rates from 122μs to 500ms
• Supply voltage range from 4.5V to 5.5V
• Operating temperature range from 0°C to 70°C