The Y1995 problem
In 1999, American media delighted in speculating on the possible Y2K doomsday. Imagine the media ruckus if those machines had been saddled with the same limitation as the Lisa, which would accept only year dates between 1981 and 1995.
This bizarre restriction stems from the Lisa's use of a primitive real-time clock chip that stored the year as a 4-bit integer--an integer from 0 to 15. Lisa hardware development solidified around 1980, so that became the base year (year 0), and 15 years after that was 1995. Why Apple forced the starting date one year ahead to 1981 is a mystery.
To keep time when the Lisa was unplugged, the Lisa clock chip depended on a four AA-cell NiCad battery pack that held a charge for only a few hours. These battery packs often busted, leaking corrosive acid over most remaining Lisas, ruining the circuit boards. (If you have a Lisa in your closet, take out the batteries now!)
On the lower right corner of the front of every Lisa sits a small white power button that becomes illuminated when the system is active. But this button does far more than power the system on or off. In fact, the button is a soft switch, which means its function is determined by software rather than a simple electrical connection.
The switch tells the Lisa to wake up from a very low power mode and restore to the screen from memory the previous computing session. The Lisa OS presents open windows and documents that you were working on before the "shutdown."
A tap on the power button began a process that shut down the system gracefully, saving all open documents and storing window and application positions for later use.
The original Mac never tried to duplicate this feature. Only now has Apple come back to the idea, as it introduced a similar function with OS X Lion in 2011. The Lisa was ahead of its time.