EPROM

EPROM emerged from a quality control crisis at Intel that became one of the most important accidental discoveries in computing history. In fall 1969, Dov Frohman, a recent hire from Fairchild Semiconductors, was investigating reliability problems with Intel's 1101 static RAM. What he found would revolutionize software development and ultimately become the ancestor of flash memory.

The adjacent possible required the floating gate MOSFET concept, proposed by Dawon Kahng and Simon Min Sze at Bell Labs in 1967. They had theorized that disconnecting a transistor's control gate—letting it "float"—would allow it to trap and hold electrical charge indefinitely. Frohman realized that if he could induce and control silicon dioxide's ability to hold charge, he could create a chip that was electrically programmable yet retained data without power—and could be erased for reprogramming.

The breakthrough was ultraviolet light. High-energy UV photons could knock electrons out of the floating gate, erasing the stored data. Frohman created what he called the Floating Gate Avalanche-injection MOS (FAMOS) device, encasing it in a package with a distinctive quartz window. Through that window, UV light could reset the chip. Through electrical programming, engineers could write new data.

Frohman debuted his prototype at the Solid-State Circuits Conference in Philadelphia in February 1971. His paper was voted best at the conference. Intel immediately commercialized the technology as the Intel 1702, a 2048-bit EPROM announced later that year. The timing was exquisite: Intel had just introduced the first commercial microprocessor, the 4004. Microprocessors needed software, and EPROM provided the perfect development environment—engineers could program, test, erase, and reprogram without soldering new chips.

Intel cofounder Gordon Moore called EPROM "as important in the development of the microcomputer industry as the microprocessor itself." The statement was not hyperbole. Before EPROM, modifying embedded software required physically replacing ROM chips. After EPROM, software development became iterative. Engineers could fail fast and fix faster.

The cascade from EPROM was profound. EEPROM followed in 1978, eliminating the UV lamp—chips could be electrically erased in-circuit. Flash memory evolved from EEPROM technology, trading granular erasability for density and speed. The flash memory in every smartphone, laptop SSD, and USB drive descends directly from Frohman's 1971 invention.

Path dependence locked in the floating gate architecture. Intel's manufacturing expertise, software development tools built around EPROM workflows, and engineers trained on the technology created switching costs that competitors couldn't overcome. When flash memory emerged, it retained the core floating gate principle Frohman had pioneered.

EPROMs quietly provided the bulk of Intel's profits into the mid-1980s, overshadowed by the microprocessor's fame but equally essential to the computing revolution. Frohman later moved to Israel, founding Intel Israel and becoming one of the most influential figures in that country's technology industry. His 1971 invention, born from investigating a manufacturing defect, made software development possible as we know it.