DRAM's inventor, 76, still going strong at IBM

Dennard's Law? It doesn't have quite the ring of Moore's Law, mostly because IBM researcher Robert H. Dennard remains unknown to the general public.

The research community, however, knows all about two significant contributions made by the 76-year-old scientist.

In the late 1960s, Dennard invented Dynamic Random Access Memory, or DRAM, the memory used in virtually all computers today.

Dennard followed in the mid-1970s with a groundbreaking paper describing how to keep shrinking transistors to build smaller, faster and less expensive chips.

Dennard's "scaling theory" ( PDF document) is often ascribed to Moore's Law, when, as Dennard modestly puts it, "scaling and Moore's Law go very well together."

For those achievements, Dennard, who celebrated his 51st year as an IBM employee this week, will receive a Medal of Honor from the Institute of Electrical Engineers next Thursday.

Fittingly, Dennard will get his Medal from IEEE one year after Intel's Gordon Moore did.

Without the invention of DRAM, computer memory might be the technology laggard that hard-disk drives and laptop batteries remain today.

As Dennard recalls it, the dominant memory used in IBM's mainframe computers of the late 1960s was magnetic core memory. Co-invented by the An Wang (later co-founder of workstation pioneer Wang Laboratories), magnetic core memory used small loops of wire to store bits of data.

Magnetic-core memory "was delicate like jewelry," Dennard said. "They were these teeny little things, almost like cheerios, but made out of ferrite [iron-based] material."

Not only was magnetic-core memory fragile, but it was expensive and slow. But it had one great advantage: It was non-volatile, meaning that you didn't need to send electric current to maintain the data.

DRAM, by contrast, seemed tricky and complicated. All of the prototypes other researchers had built up to that time were memory chips that involved multiple transistors, which made designs more complicated and expensive.

To solve this issue, some researchers were testing the use of bi-polar junction transistors. But Dennard preferred metal-oxide-semiconductor field-effect transistors, or MOSFETs, even though, he admits "MOS was definitely less advanced and more problematical. There were some basic problems to be solved to make it manufacture-able. But I still considered it more promising."

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