History Software Engineering

Williams Tube Random Access Memory (RAM) – 1946 A.D.

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Williams Tube

Frederic Calland Williams (1911–1977), Tom Kilburn (1921–2001)

“The Williams tube (sometimes known as the William–Kilburn tube), was the first all-electronic memory system, and the first that provided for random access, meaning that any location of memory could be accessed in any order.

The tube was a cathode-ray tube, such as what might be used in a World War II radar display, but modified so that dots displayed on the screen could be read by a computer. The early Williams tubes stored data one binary digit—a 0 or a 1—at a time in a rectangular array, typically 64 by 32. Developed at the University of Manchester by Frederic Williams and Tom Kilburn, the tubes were superior to the mercury delay line memory that had been used on the EDSAC and UNIVAC computers, because any bit could be accessed instantly. The bits in the delay lines, in contrast, could be read only when they had progressed through the mercury to the end of the line. But both the Williams tube and the mercury delay lines shared the property that they needed to be continually refreshed, much as do modern dynamic random access memory (DRAM) chips. Because the bits consist of stored energy that can dissipate, each bit must be continually read and then rewritten.

The IBM 701 computer used 72 Williams tubes to store 2,048 36-bit words; this electronic memory was supplemented with a spinning magnetic drum that could hold roughly four times as much memory but was much slower to access. The Williams tubes were not terribly reliable, though, and the 701 would reportedly run for only 15 minutes before it would crash due to a memory error. Indeed, the tubes were so unreliable that the Manchester Small-Scale Experimental Machine (SSEM), nicknamed Baby, was built specifically for the purpose of testing Williams tubes.

The MIT Whirlwind computer, first operational in 1949, was originally designed to use a modified Williams tube that dispensed with the need to refresh by using a second electron gun called a flood gun; the same approach would be used nearly three decades later in storage-tube displays, such as graphics terminals and oscilloscopes used in electronics labs to monitor circuits. But the modified Williams tubes cost $1,000 each and had a lifetime of roughly one month. Beset with the problems caused by these storage tubes, Whirlwind’s director, Jay Forrester (1918–2016), invented core memory as a replacement.”

SEE ALSO Delay Line Memory (1944), Manchester SSEM (1948), Core Memory (1951)

This close-up view, c. 1948, reveals dots (1s) and spaces (0s) on the face of a tube.

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Semiconductor Diode – 1874 A.D.

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Semiconductor Diode

Michael Faraday (1791–1867), Karl Ferdinand Braun (1850–1918)

“Semiconductors are curious devices: not quite conductors like copper, gold, or silver, not quite insulators like plastic or rubber. In 1833, Michael Faraday discovered that the chemical silver sulfide became a better conductor when heated, unlike metals that lose their conductivity under the same conditions. Separately, in 1874, Karl Ferdinand Braun, a 24-year-old German physicist, discovered that a metal sulfide crystal touched with a metal probe would conduct electricity in only one direction. This “one direction” characteristic is what defines diodes or rectifiers, the simplest electronic components.”

“In 1904 the British chemist John-Ambrose Fleming had invented the two-element amplifier, or ‘diode’, and a few months before DeForest the Austrian physicist Robert von Lieben had already built a three-element amplifier, or triode.” (Fair Use: B07XVF5RSP)

“Braun’s discovery was a curiosity until the invention of radio. The diode proved critical in allowing radio to make the transition from wireless telegraphy to the transmission and reception of the human voice. The diode of choice for these early radio sets was frequently called a cat’s whisker diode, because it consisted of a crystal of galena, a form of lead sulfide, in contact with a spring of metal (the “whisker”). By carefully manipulating the pressure and orientation of the metal against the crystal, an operator could adjust the electrical properties of the semiconductor until they were optimal for radio reception. Powered only by the radio waves themselves, a crystal set was only strong enough to faintly produce sounds in an earphone.”

“Crystal radio receivers were used onboard ships and then in homes until they were replaced by new receivers based on vacuum tubes, which could amplify the faint radio waves so that they were strong enough to power a speaker and fill a room with speech or music. But tubes didn’t mark the end of the crystal radio: the devices remained popular for people who couldn’t get tubes—such as on the front lines in World War II — as well as among children learning about electronics. In the 1940s, scientists at Bell Labs turned their attention to semiconductor radios once again in an effort to perfect microwave communications. In the process, they discovered the transistor.”

“Braun went on to make other fundamental contributions to physics and electronics. In 1897, he invented the cathode-ray tube (CRT), which would become the basis of television. He shared the 1909 Nobel Prize with Guglielmo Marconi (1874–1937) “in recognition of their contributions to the development of wireless telegraphy.””

SEE ALSO: Silicon Transistor (1947)

Crystal Detector, made by the Philmore Manufacturing Company. To use this device, the operator would connect a wire to each of the two flanges and press the metal “whisker” into the semiconductor crystal.”

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