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Memory technology in IBM processors has undergone a 280,000-fold increase in density, a 20,000 times decrease in power per bit, and a 10 to 100 times increase in speed during the last twenty-five years. These improvements have brought many advantages to users of information processing equipment, including a 650-fold reduction in the cost per bit of memory. During this period, processor memory technology evolved from cathode ray storage tubes in the early 1950s, through ferrite cores and thin magnetic films in the 1950s and 1960s, to bipolar and MOSFET semiconductor memories in the late 1960s through the 1970s. This paper describes these developments and the technical innovations that made them possible. It also describes continuing exploratory efforts, including work on magnetic bubbles—the newest solid state memory technology.
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