Your company will probably buy a computer within two years. Even if it already owns one, it will probably buy another.

That is the prediction of Frost & Sullivan Inc., a market research firm based in New York that recently conducted an independent survey of INC. subscribers. Of those subscribers without computers, 67% said they plan to buy one within two years. Of those who already own one, 75% said they plan to buy at least one more within two years.

Close to half the companies in the sample are already owners. Nearly two-thirds of those made their purchase within the last two years. On average, companies spent 1 1/2% of their annual sales on data processing.

Companies that already own a computer and plan to buy another have priorities that differ from those of the first-time buyer, the survey revealed. When asked to rate their top concerns in buying a computer, nonowners listed cost as most important, ease of use second, and reliability third. But those with computer experience listed reliability as the top consideration, followed by the availability of software and then cost.

Small businesses are generally happy with their computer selections. Two-thirds of current owners said that the system they bought meets their needs; 17% said it contains more capabilities than are used; and 16% said the system fails to meet their needs.

More than half the companies questioned have annual sales of less than $1 million; four-fifths have sales of less than $5 million. Sixty percent of those buying computers for the first time intend to spend less than $10,000.

One of the most complicated aspects of operating a small computer is adding peripheral equipment. One-third of current owners said that, to minimize potential problems, they wouldn't buy peripherals from anyone except the manufacturer of the original computer.