International Business Machines Corp. will roll out its new mainframe computers on Thursday, upgrading a key product line at a time when the technology giant is under pressure to show faster sales growth.

The death of the mainframe has been predicted for years, as companies opted to handle their heavy computing needs with strings of cheaper servers rather than pay a million dollars for one massive box.

The new machine, which will start shipping in September, attempts to address that challenge by letting companies use the massive computer to manage servers based on Intel Corp. or Unix technology. The software enabling the management of Unix machines will ship in the fourth quarter, and the Intel module will come out in the first half of next year.

It took three years and a $1.5 billion in investment to produce the new machine.

"The mainframe is taking a broader role in the data center," says Rodney C. Adkins, senior vice president of IBM's Systems and Technology Group.

Some people in the industry think IBM will have a hard time luring converts.

"I don't know if a lot of customers who don't have mainframes are going to get a mainframe," EMC Chief Executive Joe Tucci said in an interview.