A masked ROM (1965 Milestone) pattern is created in the factory and thus takes several weeks to produce each design iteration. User-programmable ROM (PROM) devices allow the designer to make changes in the lab. Radiation Inc. introduced a 512-bit bipolar TTL PROM (64x8) with metal fuse links connected to each bit in May 1970. A user "burned" the one-time-programmable fuses on programming units from Data I/O, Spectrum Dynamics, and others. Harris (successor to Radiation), Monolithic Memories, Motorola, and Signetics developed 1K through 16K-bit nickel-chromium fuse PROMs. AMD, Intel, and TI entered the market using alternative fuse materials and Schottky technology. (1969 Milestone)
Researchers at Bell Labs and Sperry Rand independently described alterable memory cells that stored charge in the MOS gate dielectric in 1967. At Intel in 1971 Dov Frohman used a floating (unconnected) gate for storage in the 1702 Erasable PROM (EPROM). The 2048-bits of memory could be changed and reused multiple times. The pattern was erased by exposure to ultra-violet light through a quartz window in the package. While much slower performing than bipolar devices, re-usable EPROMs found numerous applications in prototyping ROM codes for microprocessors (1971 Milestone) and microcontrollers (1974 Milestone). Intel went on to produce generations of EPROMs up to multi-million bits in density. In 1978 George Perlegos designed the Intel 2816, an Electrically Erasable PROM that eliminated the lengthy UV exposure cycle. On founding Seeq with other Intel employees in 1981, Perlegos developed an improved version that could be programmed and erased in-situ, in the system. Flash, today's most widely used non-volatile memory (NVM) form, was developed in 1984 by Fujio Masuoka of Toshiba and commercialized by Intel in 1988.
D. Kahng, D, and Sze, S. M. "A floating-gate and its application to memory devices," The Bell System Technical Journal, Vol. 46, No. 4 (1967) pp.1288–1295.
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Augarten, Stan. "A Piece of Electronic Magic," State Of The Art: A Photographic History of the Integrated Circuit. (New Haven & New York: Ticknor and Fields, 1983) p. 32.
Brown, William D. and Brewer, Joe E. (Editors) Nonvolatile Semiconductor Memory Technology: A Comprehensive Guide to Understanding and Using NVSM Devices. (Wiley-IEEE Press, October 15, 1997).
"Fujio Masuoka: Thanks for the Memory. Voices of Innovation," Business Week (April 3, 2006).