At 10:58 this morning, all was not well at the New York Stock Exchange, the world's biggest securities market.

The big computer that produces the so-called ticker tape broke down, and with it so did stock trading across the country.

Stock exchange officials were lucky. The computer breakdown happened on Columbus Day, a day when trading was reduced by three-day vacations.

Perhaps even some investors were lucky. Stock prices had been drifting down aimlessly in early trading. The hour-long lull seemed to put some juice into the market. The Dow Jones industrial average closed up 9.22 points on the day.

But other investors clearly were inconvenienced. From 11:11 a.m. -- when NYSE officials decided the problem was serious enough to halt trading -- until 12:05 p.m. -- when the bell clanged to signal a resumption of activity -- most investors who wanted to buy or sell a stock listed on a major or regional stock exchange could not.

"If someone wanted to buy 1,000 shares of IBM, we would have advised them to wait until the central market was functioning again," said Patrick C. Ryan, chief of trading at the Washington brokerage firm Johnston, Lemon & Co. Inc.

Of course, if a buyer was insistent enough, Ryan conceded, "we would have tried to do a trade wherever we legally could." That would have had to be in the so-called over-the-counter market where some brokers continue to make limited independent markets in stocks that are traded on major exchanges.

Over-the-counter trading was not affected by the computer breakdown in New York. The automated quotations system run by the National Association of Securities Dealers continued to function.

John Weithers, president of the Midwest Stock Exchange, said the Chicago trading floor shut down because of an inability to get "last sale" reports on price and volume. Like all regional exchanges, most of the Midwest's trading occurs in stocks that also are listed on the NYSE and the Amex.

All trading in stocks listed on those two exchanges is reported to a nation-wide consolidated tape.