MOS DRAM

MOS DRAM emerged from a living room eureka on November 9, 1966. Robert Dennard, an IBM engineer discouraged after seeing a competitor's memory approach, went home and conceived the one-transistor, one-capacitor architecture that would enable personal computing. The insight was elegant: store binary data as charge on a capacitor, use a single MOSFET transistor to gate access. Previous semiconductor memory required six transistors per bit—too expensive to compete with magnetic core. Dennard's design achieved the same function with one-sixth the components.

The adjacent possible had been assembling since 1959, when Mohamed Atalla and Dawon Kahng invented the MOSFET at Bell Labs. By the mid-1960s, IBM's Thomas J. Watson Research Center had built world-class MOS fabrication capabilities. Magnetic core memory—women with microscopes threading wires through tiny ferrite rings—had hit its economic floor. MIT's 1967 Moby Memory cost $380,000 for 256K words and filled a cabinet. The pressure for semiconductor alternatives was intense.

Intel commercialized DRAM first. The 1103, launched in October 1970, used a three-transistor design for manufacturability. At $60 per chip—roughly one cent per bit—it undercut core memory costs that could not fall further. Gordon Moore called it the chip that really got Intel over the hump to profitability. By 1972, fourteen of eighteen mainframe manufacturers relied on the 1103.

The cascade created modern computing. The Altair 8800 in 1974, Apple I in 1976, Apple II in 1977—each combined microprocessors with DRAM to create affordable personal computers. Density quadrupled every three years: 1K bits in 1970, 4K by 1974, 64K by 1980, reaching 1 gigabit by 2000. Dennard's second contribution, scaling theory published in 1974, provided the roadmap: shrink transistors by 30%, get 40% faster at half the power density. That roadmap guided semiconductor manufacturing for thirty years. Today's data centers average 2.5 petabytes of DRAM per facility, all descended from Dennard's evening insight.