It was the 21st leap second since the first one was added on June 30, 1972. This tiny adjustment is just one more place where computers can go wrong in keeping time and dealing with the vagaries of the calendar. By now, everyone has probably heard about the problems that may arise when the year 2000 arrives. Any computer system that stores or handles fewer than the full four digits of the year will have to deal with a year number that is smaller than its predecessor. Subtractions to determine the time interval will yield negative numbers, with unexpected and potentially disastrous consequences.
Problems involving dates and time go beyond the unfortunate use of two-digit years.
Indeed, synchronizing human time with computer time presents programmers with a host of difficulties. From a computer programmer's point of view, such quaint conventions are at best a nuisance and at worst a nightmare. Every four years, for example, computers of all sorts fail because unwary software developers forgot that February has 29 rather than 28 days. In 1992, for example, legions of ATM machines neglected to acknowledge the extra day and ended up scrambling the data encoded on cards of customers who used an ATM on February 29. Inevitably, new leap-year problems surfaced in 1996, and more such bugs will undoubtedly add to the confusion in the year 2000.