Every time you set up a computer, you must set its clock. What's worse , computer clocks are imperfect, so they drift from the true time ”and they drift at different rates. The result is that, on a network of any size , a few weeks (or possibly just a few hours) after you've set all the computers' clocks to the same time, they'll show annoying differences. Daylight Savings Time can also cause problems, because you'll have to set the computers' clocks again or allow the computers to adjust their own times ”a process that can itself cause problems if a computer has more than one OS installed on it. All told, keeping all your systems' clocks synchronized can be an administrative headache . Fortunately, a class of programs exists to help work around this problem: time servers. These programs deliver accurate time measurements to their clients, so setting up a central time server and configuring clients to use it can keep all your computers set to the same time. You can even have your central time server synchronize itself to an outside time server that sets its time using an atomic clock, thus allowing for very accurate time settings across your entire network.