Inventor of the Week Archive
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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
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
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