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Random Access Memory

Robert Dennard invented one of the most significant advances in computer technology: dynamic random access memory, best known as "RAM."

Dennard was born in Terrell, Texas in 1932. He receieved his BS (1954) and MS (1956) in Electrical Engineering from that state's Southern Methodist University, and in only two more years earned a PHD in the same field from Carnegie Technical Institute (1958). He then became a Staff Engineer in the Research Division of IBM, where he planned to spend "a couple of years at most" learning the ropes. Forty-two years later, Dennard remains one of IBM's most honored employee-engineers.

Dennard began his career in an era when technicians fed punchcards into computers so big that they filled rooms and required their own air conditioning systems. The first commercially available computer, UNIVAC, had been produced in 1951; but the notion of an average person owning a computer was still fantastic. In 1959, Jack Kilby's invention of the integrated circuit constituted the first step toward the feasible personal computer, because the microchip made it possible drastically to reduce the size of a computer's main memory storage unit. In 1966, Dennard took the second step, when he invented one-transistor Dynamic Random Access Memory (or DRAM, better known simply as RAM).

That year, Dennard's research team was working on field-effect transistors (FETs) and integrated circuits, using the then standard six-transistor memory cell for each bit of data. After an in-house presentation by a rival IBM team piqued his sense of competition, Dennard set out to streamline the memory cells that he was working on.

At that time, RAM was a known and used concept: memory reserved for writing to and reading from in a temporary fashion, to be erased every time the computer is turned off. However, in the mid-1960s RAM required an elaborate system of wires and magnets that was bulky and power hungry, negating in practice RAM's theoretical efficiency. Dennard's revolutionary achievement was to reduce RAM to a memory cell with only a single transistor. His key insight was that it should be possible to store binary data as a positive or negative charge on a capacitor. After several months of experimenting, Dennard had reduced his RAM cell to a small capacitor and a single field-effect transistor gating the flow of data to and from a data line. The ultimate effect of Dennard's invention was that a single chip can hold a billion or more RAM cells in today’s computers.

Dennard won a patent for his one-transistor RAM in 1968. By the early 1970s, it was commercially available, and by the mid-1970s, it was standard in virtually all computers. When personal computers became thinkable, Dennard's RAM system allowed them to perform complex operations and still fit on a desktop --- and later to become affordable. The rise to prominence of the PC made Dennard a natural choice for the National Medal of Technology (1988).

Since then, "How many megabytes of RAM. . .?" has become a commonplace question; and the answers are more impressive for each new generation of computers. Leaving the computers aside, $25 billion worth of RAM, in and of itself, is sold every year.

Meanwhile, Robert Dennard, since 1979 a Fellow of IBM's T.J. Watson Research Center, has continued his career of invention, in refinements to RAM, specialized FETs, and low-voltage, high-performance operation of circuits. He is also a co-author of "scaling theory," an analytical framework for studying the special conditions of engineering microchips in ever more microscopic dimensions.

[March 2000]