We are always grateful to the readers who write us either by fax, e-mail, or snail mail ? about this column.

The volume of our correspondence has grown sharply in recent years, no doubt because e-mail makes it so easy to send a letter. We try hard to answer everyone, but some weeks it is just not possible to respond to each comment or query. So we'll use this column to reply to some of the most common questions in our mailbag.

One of the hottest topics in our mail queue recently has been the famous "millennium bug," also known as the "Year 2000 problem" or the "Y2k." The problem is that some large office and research computers were programmed long ago to treat the year field in a date as a two-digit number ? that is, 1998 is stored as "98." The computer just assumes that the first two digits of the year are "19."

(This programming peculiarity, by the way, was not the fault of stupidity or laziness. It's just that memory space in computers used to be expensive and limited, so early programmers were constantly using such tricks to reduce memory usage. Reducing a four-digit year to a two-digit number was considered an act of genius at the time.)

But now that people routinely have credit cards, mortgages, contracts, etc., that extend to the 21st century, a two-digit year is not enough. If your bank's computer sees that you have a loan payment due on 1/15/00, it may decide that you owed a payment in January of 1900, and assess 100 years of late fees.

"Y2k" is a big problem for corporations and government offices that use huge, old mainframe computers. It is not a problem for a personal computer user. Just about every PC and software program sold for the past 15 years has been programmed with the new century in mind. We even fired up an old Heathkit computer, 1980 vintage, running the antique CP/M operating system (this was the predecessor of DOS, which was the predecessor of Windows), and it had no trouble with the year 2000.

You can check this if you like by changing the "system clock" on your PC to 11:55 p.m. Dec. 31, 1999, and waiting five minutes to see what happens. What you'll find, we'll bet, is that all your software will glide smoothly into the new century without a glitch. If you do find a piece of software so old it doesn't know about the 21st century, the maker will almost certainly have issued an upgrade by now.


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