With its carpeted cubicles and computer terminals, Stillwater Data Processing Systems Inc. looks like any other modern, high-technology office. At 5 p.m., however, the employees go home not to their wives, but to their warden.

SDPSI may be the only private corporation operating from behind the walls of a maximum-security prison, the Minnesota Correctional Facility-Stillwater. Founded by several Stillwater inmates in 1974, the company supplies software for such corporate heavyweights as Northern Telecom, 3M, and Control Data. It has eight inmate employees and a board of directors composed of 13 businessmen. Don Richards, a technology consultant in the data processing field for 20 years, is the chief operating officer.

In a service business where the pros are cons, there can be some problems. If the display terminals are dark for a day, for example, a lockup is more likely to be the reason than a brownout. "I can't filter the prison out of this place 100%," says Richards. "If I could, my job would be a whole lot easier."

The lack of mobility is another obstacle. "Sometimes it's real inconvenience that the fellows doing work on our project can't come out here to meet with us," says Jerry Caldwell, performance information specialist at 3M. On the other hand, Caldwell admits, "It's become routine for me to go out to the prison. Sometimes, on my way in, I'll see someone coming by in the corridor and I'll sort of wonder what he did to be there."

Jobs at SDPSI are in great demand. To be considered, an inmate must have completed an accredited data processing course (several are offered at Stillwater); must show a clean behavior record for at least 6 consecutive months immediately prior to application; cannot have been convicted of any computer-related crime, or of embezzlement; and, to avoid rapid turnover, must have a minimum of 15 months of mandatory jail time left to go.

"When employees come into the company, we demand, so to speak, a flip of the switch in the head -- prison is out there; in here, you're at work," explains Richards. The physical amenities of the office help, such as private spaces, air conditioning, and phone service, as does the interaction with Richards and the board members.

Upon release, all but one of the SDPSI alums have gone straight -- and in many cases, straight into high-tech jobs, sometimes rising as high as senior project manager.

Stillwater Data faces all the problems of growing companies, plus the restraints of the prison that prevent it from branching into more sophisticated, time-sensitive areas of their customers' work. The professional managers are exploring new directions: Inmates are writing programs for microcomputers now, and they may produce software for small companies in the future. "In the long run," says board member Donald Gray, a data-processing consultant, "this company, just like any other company, will succeed or fail based on economic factors and on how well the job gets done."