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The technology behind the modem -- a device that converts data into signals that can be passed through channels such as phone lines -- has existed in primitive forms since the late 1940s. But in those days, phone lines carried data signals inconsistently, and information was transmitted slowly.

While working at the Massachusetts Institute of Technology's Lincoln Laboratory in 1958, Mr. Rosen and a colleague, Jack Harrington, patented a device that rapidly transmitted large amounts of data over phone lines.

Their invention, "Method of Land Line Pulse Transmission," helped expand computer networks nationwide by significantly accelerating the flow of data over phone lines.

"One of my colleagues said, 'Oh, you're going to get rich on this,' " Mr. Rosen said in a 2004 interview with IEEE, the organization formerly known as the Institute of Electrical and Electronics Engineers.

But the patent's wording was too constrained -- the work of an inept lawyer, Mr. Rosen often said -- which allowed competitors such as AT&T's Bell Labs to create their own modems by making only minor adjustments to the patented design. Thus, Mr. Rosen never made the fortune he thought he deserved when high-speed modems based on his work began popping up across the United States.

Nonetheless, Mr. Rosen's system was a crucial addition to a landmark Army defense project during the Cold War. The SAGE program, or Semi-Automatic Ground Environment, was a series of more than 100 radar installations spread across the northern border of the United States. Each station sent data about incoming planes, such as Russian bombers loaded with nuclear weapons, to centers around the country at a rate of more than 1,800 bits per second through Mr. Rosen's modems.

The standard maximum speed for data transmission was about 600 bps, but Mr. Rosen's breakthrough technology allowed the military to monitor U.S. air space nearly in real time.

In 1979, for his leadership and contributions in military communications, Mr. Rosen was made a fellow of the IEEE, one of the most prestigious honors for engineers.

Paul Rosen was born in Boston on Jan. 4, 1922. His parents were Jewish immigrants from Russia, and he grew up in ghettos in suburban Boston. His father's first job in the United States was washing milk cans at a dairy.

Mr. Rosen said he became fascinated with engineering while toying with old crystal radios as a teenager. At what is now Tufts University, Mr. Rosen said, he received a "lousy education" and made money working in the school's machine shop, where he made cast-iron ingots for 40 cents an hour. He graduated with a bachelor's degree in electrical engineering in 1944 and joined the Navy during World War II.

After sporadic training that included stints as an enlisted sailor and deck officer, Mr. Rosen spent the rest of his Navy service in Guam with a logistics company, supervising the loading and unloading ships.