Ask Robert Dennard about the invention of DRAM, and he will probably do three things.
First, he will show you the patent notebooks IBM encouraged its inventors to keep, which hold all his ideas about dynamic random-access memory, meticulously dated and witnessed by other people, ”to make sure we had proof of our inventions.” He stores these pristine notebooks in an armoire under a wall crowded with his awards.
Second, he will spend half an hour showing you how he had the revolutionary idea of substituting a single transistor and a single capacitor for the memory technology then being usedmagnetic rings, like miniature Cheerios, each of which stored one bit based on the polarity of its magnetic field. He will draw the circuit diagram for the one-transistor DRAM, including every amplifier, data line, and inverter.
Finally, he will comment on a certain online article that suggests that Intel engineers, rather than Dennard and IBM, should be credited with the invention of DRAM. Intel released a three-transistor DRAM in 1970, three years after Dennard entered the one-transistor DRAM into his patent notebook. The misattribution annoys Dennard to no end: ”They asked someone from Intel who worked on the chip, ’Did you invent DRAM?’ And he said, ’We don’t care about inventions. We care about products.’ ” Dennard pauses. ”A lot of people think Intel invented DRAM, because they were the first to come out with something labeled dynamic RAM,” he says. Just about everywhere else, Dennard is credited as the father of DRAM, and for that achievement he is being awarded this year’s IEEE Medal of Honor.
The wrestling over who gets credit is no hopelessly irrelevant teapot tempest. Random-access memory inhabits pretty much everything that has electrons coursing through it: your laptop, car, game console, digital camera, and cellphone. The amount of RAM in these devices might even be taken as a kind of shorthand for their approximate level of performance. That’s because ever-increasing memory capacity is one of the key factors driving the evolution of most electronics.
Semiconductor memory is now a large extended familyincluding EEPROM (electrically erasable programmable read-only memory) and NAND flasheach category with different drawbacks and benefits. But dynamic random-access memory is an important ancestor. ”Random access” means what it says: A microprocessor can withdraw any stored ”word” (8 bits of data) from this memory in any order.
In Dennard’s one-transistor DRAM, each bit of data is stored separately inside its own capacitor. A single transistor controls both reading and writing. A charged capacitor means ”1,” and an uncharged capacitor means ”0.” The word dynamic in the name derives from the fact that the act of reading the bit discharges it and it must be rewritten back into memory. A capacitor’s charge eventually wanes, so the memory must be reinfused with fresh charge several times per second to prevent it from losing information. That fact led one researcher to joke that Dennard had won prestigious awards not for his invention but rather for having the temerity to refer to such a thing as ”memory.”
Amazingly, in an industry defined by its constant advances and compulsory forward movement, the one-transistor DRAM has endured for 40 years.
In 1958, when Dennard walked into IBM’s still-unfinished Thomas J. Watson Research Center for his first day at work, he didn’t know exactly how a transistor worked. In those days, not too many engineers actually did. Dennard, fresh out of Pittsburgh’s Carnegie Institute of Technology (now Carnegie Mellon University), had just earned a Ph.D. in electrical engineering after completing undergraduate and master’s work in EE at Southern Methodist University, in Dallas.
But what he recalls most fondly is his first educational experience, one from a bygone era. ”At the National Inventor’s Hall of Fame, a bunch of us guysall very successfulwere having a conversation, and we found out that all of us went to one-room schoolhouses,” he says. ”That was the common denominator.”
Growing up in a 5000-person farm community near the Louisiana border of Texas, that’s all there was. No Baby Einstein classes for Dennard, no Mozart symphonies on a phonograph. The Depression was just ending; his community hadn’t been electrified. ”We survived just fine,” he says, adding that the secret to his success was that he had a lot of spare time as a child. ”I learned everything very slowly and concentrated deeply,” he recalls.
In those days, he wasn’t interested in science or engineering at all. ”I had a crystal radio,” he declares, ”but I never got that thing to work.” What he loved was science fiction; he devoured old anthologies that included authors like Edgar Rice Burroughs and H.G. Wells. ”One story really influenced me,” he recalls. ”It was about probability.” The short story, ”Inflexible Logic,” by Russell Maloney, was published in 1940. To test the theory that patterns would emerge out of randomness, a man assembled six monkeys and set them to typing, to see if they would come up with anything rational or intelligible. After quite a short time, the monkeys began to write some very familiar prose. The man shared the results with his friend, a professor.
”And the monkey was coming up with great stuff, and [the professor] was walking around scratching his head and thinking, It couldn’t have happened so soon.” Dennard pauses and laughs uproariously. ”So he shoots the monkey!”
Science fiction was as close as he got to an interest in science until he took physics classes at SMU, which he attended on a dual academic/band scholarship as a French horn player. He liked his physics classes, particularly the emerging field of semiconductor physicsso much so that he decided to pursue a doctorate in electrical engineering, which was then an interesting discipline that in some ways hadn’t quite found itself. ”I had some advanced physics courses, solid-state materials, and so forth,” he says, ”but I still didn’t understand exactly how a transistor operated.” Armed with his Ph.D., he followed some friends to IBM, which was on a research-scientist hiring binge. He figured he’d stay for a few years. Fifty-one years later, he’s still there.