NEW YORK -- When International Business Machines Corp. announced its new personal computer at a press conference here Tuesday, few people paid attention to Jim Kimsey, the president and chief executive officer of Quantum Computer Services Inc. of Vienna. At the end of the event, as key IBM executives were besieged with questions, Kimsey strode out of the auditorium alone.

"None of those people knew who I was even after I was introduced," Kimsey said later. "And I'm sure they'd never heard of Quantum."

That is likely to change. IBM's selection of the privately held five-year-old company as a provider of built-in information services for the PS/1 personal computer, thrusts Quantum into an unaccustomed spotlight.

Quantum, with $22 million in annual revenue and 170 employees, has grown rapidly into a significant player in the "on-line services" market, providing educational and entertainment software programs to more than 125,000 subscribers.

Subscribers to on-line services are able to receive weather reports, make airline reservations, access bank accounts, play computer games and correspond electronically with one another over the telephone lines that link their computers. But the use of such services has trailed the spread of personal computers, in part because customers had to buy separate communications devices called modems to gain access to the services.

IBM hopes to remedy that situation with its PS/1, the first home computer to contain both a built-in modem and on-line service software programs. Quantum has tailored its Promenade software to what IBM's research indicated consumers wanted in a home computer, including a 20-volume, continually updated encyclopedia, a software library with more than 7,000 titles that members can transfer instantly to their PS/1 and an electronic mail system linking subscribers, who can be connected for as little as $7.50 an hour.

At Quantum, which also offers customized services for Apple, Tandy and Commodore computers, employees act as hosts for live nationwide computer game shows, coordinate the scheduling of events such as trivia games and educational programming, and award prizes such as microwave ovens and software programs.

In addition to Quantum, other major players in the on-line services market are Compuserve, a division of H&R Block Co., with 550,000 subscribers; Prodigy, a partnership between IBM and Sears, Roebuck & Co. that has approximately 270,000 subscribers; and GEnie, a division of GEInformation Services, which has 200,000 subscribers. Prodigy, designed to provide subscribers with such services as stock market trading and airline reservations, is the other on-line service offered with the PS/1. So how did Quantum wind up inside the PS/1 while most of its bigger competitors were left on the outside looking in?

Quantum officials say it was the company's nimble reflexes, which enabled it to customize a service for the new IBM product faster, and its growing reputation in the market.

"We're an independent company with a proven track record of being able to do big things in a short period of time and do them successfully," said Jean Wackes, Quantum's vice president of marketing. "There's no bureaucracy to cut through here. We've built a customized software service for IBM and given them what they want. They saw that we could make things happen."

That style follows the design of Kimsey, a 50-year-old United States Military Academy graduate who entered the restaurant business in Washington in 1970, after two tours as a ranger in Vietnam. Starting with $2,000 saved from his second tour, he eventually owned four successful restaurants before selling three because he was "getting bored." He then teamed up with one of his West Point classmates who was investing in a high-tech company, and that transaction eventually led to the creation of Quantum.

Quantum's virtues were not immediately obvious to IBM, though. According to Steve Case, executive vice president of Quantum, IBM's PS/1 team had only a vague awareness of the Vienna company, but Quantum set about changing that.

"When we were talking to consumers about what they wanted in a computer, a lot of them said they wanted to have someone technical sit next to them and teach them about the machine," said Tony Santerelli, vice president of new business development for IBM's entry system division and head of the team that developed the PS/1. "That was economically impractical, even for us. So we looked for the next best thing -- bringing the technological help into the home. We also heard a lot from parents of college kids about how they needed something to help them through their all-nighters. Promenade met that need with its encyclopedia. Essentially, Promenade had all the academic and entertainment services we wanted to complement Prodigy."

"IBM picked Quantum because it and Prodigy have had a relationship for a year," said Karen Nielsen, an analyst at New York-based Link Research Inc. "Each advertises in the other's monthly newsletter. Quantum argued that the two services complement each other and that users would benefit from a dual subscription. So it doesn't surprise me at all that they hooked up. Quantum very firmly believes in the intelligent personal computer as the key access device to on-line services."

The PS/1, priced from $999 to $1,999, will test that belief. Now sold only in Chicago, Minneapolis-St. Paul and Dallas, the machine will be available nationally in September. If that event causes an explosive demand for the computer, Quantum may expand. Case said the company expects to hire more people, but not that many because its current infrastructure allows it to simply repackage new products rather than develop them from scratch. According to Wackes, Quantum's current inventory has plenty of excess capacity to handle any increased demand.

But the company is not staking its existence on the success or failure of the PS/1.

"This is a signal, catalytic event for the industry because IBM is redefining the home computer market," Kimsey said. "But it's not a make-or-break deal for us. We're not expecting more than $1 million in revenue from it this year. Down the road, we don't know how much it will be. If the PS/1 doesn't work, we're not in big trouble.

"The PS/1 deal certainly raises our credibility. That should really help us with our overall strategy, which is to be woven through the fabric of the on-line services industry as it starts to unfold. Credibility is the name of the game. And when IBM puts a tiny little company inside its box {computer}, that really tells you something."