Magnetic core memory reborn

Posted on Feb 6, 2014

Magnetic core memory was the most widely used form of digital computer memory from its birth in the early 1950s until the era of integrated-circuit memory began in the early 1970s. Aside from being extremely reliable, magnetic core memory is an appealing technology because it is based on a very simple idea. A magnetic core is a ring of ferrite material. It can be

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permanently magnetised either clockwise or anti-clockwise about its axis just as a vertical bar magnet can be magnetised up or down. We can then turn a magnetic core into a bit of digital memory by letting these two magnetisation states correspond to 0 and 1. The core needs no power to retain its data. In other words, core memory is a form of non-volatile storage like modern hard disk drives, although in its day it fulfilled the high-speed` role of modern RAM. With many such cores, large memory modules were made, such as this example from a CDC machine of the mid-1960s. The right-hand image shows a close-up of the cores themselves. As the technology developed [1], the cores shrank from c. 2mm diameter in the early 1950s to c. 0. 4mm by the early 1970s. Access speeds rose at the same time, from about 200kHz to over 1MHz, and core memory modules were manufactured with as many as over half a million cores. Furthermore, as recently as 2004, a magnetic core memory system was found still in service in a telephony control system. Magnetic core memory continues to capture the imaginations of modern enthusiasts [2], [3], and it is also the origin of the term core dump, to mean an on-disk image of the main memory of a process. The Arduino, whose Duemilanove version is shown above [5], is an open-source physical computing device. It has removed many of the hurdles for people wishing to explore embedded microprocessing. An Arduino is...

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