In our described the rise of automatic telephone exchanges, which were controlled by relay circuits. This time we want to talk about how scientists and engineers developed relay circuits in the first - now forgotten - generation of digital computers.
Relay at its zenith
If you remember, the operation of a relay is based on a simple principle: an electromagnet operates a metal switch. The idea of ββthe relay was proposed independently in the 1830s by several naturalists and entrepreneurs in the telegraph business. Then, in the middle of the XNUMXth century, inventors and mechanics turned the relay into a reliable and indispensable component of telegraph networks. It was in this area that the life of the relay reached its zenith: it was miniaturized, and generations of engineers created a myriad of designs, formally trained in mathematics and physics.
At the beginning of the 1870th century, not only automatic switching systems, but almost all telephone network equipment contained one or another type of relay. One of the earliest uses in telephony dates back to the XNUMXs, in manual switches. When the subscriber twisted the handle of the phone (magneto handle), a signal was sent to the telephone exchange, turning on the blender. Blenker is a relay that, when triggered, on the switching table at the telephone operator, a metal shutter fell, which indicated an incoming call. Then the lady operator inserted the plug into the connector, the relay was reset, after which it was possible to raise the damper again, which was held in this position by an electromagnet.
By 1924, two Bell engineers wrote, a typical manual telephone exchange served about 10 subscribers. Her equipment contained 40-65 thousand relays, whose total magnetic force was "sufficient to lift 10 tons." In large telephone exchanges with machine switches, these characteristics were multiplied by two. Many millions of relays were used throughout the US telephone system, and their number increased steadily as telephone exchanges were automated. One telephone connection could serve from a few to several hundred relays - depending on the number and equipment of the telephone exchanges involved.
The factories of Western Electric, Bell Corporation's manufacturing arm, produced a huge range of relays. Engineers have created so many modifications that the most sophisticated dog breeders or pigeon lovers would envy this variety. The speed of operation and sensitivity of the relay were optimized, the dimensions were reduced. In 1921, Western Electric produced almost 5 million relays of one hundred basic types. The most massive was the Type E universal relay, a flat, almost rectangular device that weighed several tens of grams. For the most part, it was made from stamped metal parts, that is, it was technologically advanced in production. The case protected the contacts from dust and induced currents from neighboring devices: usually the relays were mounted close to each other, in racks with hundreds and thousands of relays. In total, 3 thousand variants of Type E were developed, each of which differed in winding and contact configurations.
Soon, these relays began to be used in the most complex switches.
Coordinate switch
In 1910, Gotthilf Betulander, an engineer at the Royal Telegrafverket, the state-owned corporation that controlled most of the Swedish telephone market (almost all for decades), had an idea. He believed that he could greatly improve the efficiency of the Telegrafverket's operations by building automatic switching systems entirely based on relays. More precisely, on relay matrices: lattices of steel bars connected to telephone lines, with relays at the intersections of the bars. Such a switch should be faster, more reliable and easier to maintain than systems based on sliding or rotating contacts.
Moreover, Bethulander came up with the idea that it is possible to separate the parts of the system responsible for selection and connection into independent relay circuits. And the rest of the system should be used only to establish a voice channel, and then be freed to serve another call. That is, Betulander came up with the idea, which was later called "common control" (common control).
He called the circuit that stores the number of the incoming call "recorder" (another term is register). And the scheme that finds in the grid and "marks" the available connection, he called the "marker". The author has patented his system. Several such stations appeared in Stockholm and London. And in 1918, Bethulander learned about an American innovation: the crossbar switch, created by Bell engineer John Reynolds five years earlier. This switch was very similar to the design of Betulander, but it used n+m maintenance relay n+m matrix nodes, which was much more convenient for the further expansion of telephone exchanges. When a connection was established, the holding bar clamped the "fingers" of the piano strings, and the select bar moved across the matrix to connect to another call. The following year, Bethulander incorporated this idea into his commutator design.
But most engineers considered Bethulander's creation strange and unnecessarily complicated. When it came time to choose a switching system to automate the networks of the largest Swedish cities, Telegrafverket opted for a design developed by Ericsson. Bethulander switches were only used in small telephone exchanges in rural areas: the relays were more reliable than the motorized automation of Ericsson switches and did not require maintenance technicians at each exchange.
However, American telephone engineers had a different opinion on this matter. In 1930, Bell Labs arrived in Sweden and were "very impressed with the parameters of the coordinate switching module." Upon their return, the Americans immediately began working on what would become known as "coordinate system No. 1," replacing panel switches in large cities. By 1938, two such systems were installed in New York. They soon became standard equipment for city telephone exchanges, until over 30 years later they were replaced by electronic switches.
The most interesting component of crossbar #1 was the new, more complex marker developed at Bell. It was intended to search for a free route from the caller to the called through several coordinate modules connected to each other, due to which a telephone connection was created. Also, the token had to test each connection for the state of "free" / "busy". This required the application of conditional logic. As historian Robert Chapuis wrote:
The choice is arbitrary because a free connection is only held if it provides access to a rail that has a free connection to the next level as its output. If several sets of connections satisfy the desired conditions, then the "priority logic" (preferential logic) selects one of the [existing] smallest connections ...
The crossbar is a perfect example of cross-fertilization of technological ideas. Betulander created his all-relay switch, then improved it with a Reynolds switch matrix and proved the resulting design to work. AT&T engineers later redesigned this hybrid switch, improved it, and created the No. 1 coordinate system. This system then became a component of two early computers, one of which is now known as a milestone in the history of computing.
Mathematical calculations (Mathematical labor)
To understand how and why relays and their electronic cousins ββhelped revolutionize computing, we need a short digression into the world of mathematical computing. After it, it will become clear why there is a hidden demand for optimization of computing processes.
By the beginning of the XNUMXth century, the entire system of modern science and engineering was based on the work of thousands of people who performed mathematical calculations. They were called by computers (computers)[To avoid confusion, hereinafter the term will be used calculators. β Note. per.]. Back in the 1820s, Charles Babbage created (although his apparatus had ideological predecessors). Its main task was to automate the construction of mathematical tables, for example, for navigation (calculation of trigonometric functions by polynomial approximations at 0 degrees, 0,01 degrees, 0,02 degrees, etc.). There was also a great demand for mathematical calculations in astronomy: it was necessary to process the raw results of telescope observations in fixed regions of the celestial sphere (and the dependence on the time and date of observations) or to determine the orbits of new objects (for example, Halley's comet).
Since the time of Babbage, the need for computers has grown exponentially. Electricity companies needed to understand the behavior of power transmission systems with extremely complex dynamic properties. Cannons made of Bessemer steel, capable of throwing projectiles over the horizon (and therefore, due to direct observation of the target, they were no longer aimed), required increasingly accurate ballistic tables. New statistical tools that involved a large amount of mathematical calculations (for example, the method of least squares) were increasingly used both in science and in the growing state apparatus. Universities, government offices, and industrial corporations sprang up computing departments that usually recruited women.
Mechanical calculators only facilitated the task of computing, but did not solve it. Calculators accelerated arithmetic operations, but any complex scientific or engineering task required hundreds or thousands of operations, each of which the calculator (human) had to perform manually, carefully recording all intermediate results.
Several factors contributed to the emergence of new approaches to the problem of mathematical calculations. Young scientists and engineers, who painfully calculated their tasks at night, wanted to rest their hands and eyes. Project managers were forced to shell out more and more money for the salaries of numerous calculators, especially after the First World War. Finally, many advanced scientific and engineering problems were difficult to compute by hand. All these factors led to the creation of a series of computers, work on which was carried out under the direction of Vannevar Bush, an electrical engineer at the Massachusetts Institute of Technology (MIT).
Differential Analyzer
Up to this point, history has often been impersonal, but now we will talk more about specific people. Glory bypassed the creators of the panel switch, the Type E relay and the fiducial marker circuit. Not even biographical anecdotes have been preserved about them. The only publicly available evidence of their life is the fossilized remains of the machines they created.
Now we can get a deeper understanding of people and their past. But we will no longer meet those who worked hard in the attics and workshops at home - Morse and Vail, Bell and Watson. By the end of World War I, the era of heroic inventors was almost over. Thomas Edison can be considered a transitional figure: at the beginning of his career he was a hired inventor, and towards the end he became the owner of an "invention factory". By that time, the development of the most notable new technologies had become the domain of organizationsβuniversities, corporate research departments, government laboratories. The people we will talk about in this section belonged to such organizations.
For example, Vanivar Bush. He arrived at MIT in 1919 when he was 29 years old. A little over 20 years later, he was among the people who influenced US involvement in World War II, and helped increase public funding, which forever changed the relationship between government, academia, and the development of science and technology. But for the purposes of this article, we are interested in a series of machines that have been developed in the Bush laboratory since the mid-1920s and were intended to solve the problem of mathematical calculations.
MIT, which had recently moved from central Boston to the Charles Riverfront in Cambridge, was closely tied to the needs of the industry. Bush himself, in addition to his professorship, had financial interests in several electronics businesses. So it shouldn't surprise you that the problem that led Bush and his students to work on the new computing device originated in the power industry: to simulate the behavior of transmission lines under peak load conditions. Obviously, this was only one of the many possible applications of computers: tedious mathematical calculations were carried out everywhere.
Bush and his colleagues first built two machines, which they called product integraphs. But the most famous and successful MIT machine was another - differential analyzercompleted in 1931. He solved problems with the transmission of electricity, calculated the orbits of electrons, the trajectories of cosmic radiation in the Earth's magnetic field, and much more. Researchers around the world who needed computing power created dozens of copies and variants of the differential analyzer in the 1930s. Some - even from Meccano (the English analogue of the American children's designers of the brand ).
The differential analyzer is an analog computer. Mathematical functions were calculated using rotating metal rods, the rotation speed of each of which reflected some quantitative value. The motor actuated an independent rod - a variable (usually it represented time), which, in turn, through mechanical connections, rotated other rods (different differential variables), and a function was calculated based on the input speed of rotation. The calculation results were drawn on paper in the form of curves. The most important components were integrators - wheels that rotated with disks. Integrators could calculate the integral of a curve without tedious manual calculations.
Differential analyzer. Integral module - with a raised lid, from the side of the window there are tables with the results of calculations, and in the middle - a complex of computing rods
None of the analyzer components contained discrete switching relays or digital switches of any kind. So why are we talking about this device? The answer is fourth family car.
In the early 1930s, Bush began courting the Rockefeller Foundation to get funding to further develop the analyzer. Warren Weaver, head of the foundation's natural sciences department, was initially unconvinced. Engineering was not his area of ββexpertise. However, Bush touted the limitless potential of his new machine for scientific applicationsβespecially in mathematical biology, Weaver's favorite project. Bush also promised numerous improvements to the analyzer, including "the ability to quickly switch the analyzer from one problem to another, like a telephone switchboard." In 1936, his efforts were rewarded with an $85 grant to build a new device that was later called the Rockefeller Differential Analyzer.
As a practical calculator, this analyzer was not an outstanding breakthrough. Bush, who became vice president of MIT and dean of the engineering department, could not devote much time to leading development. In fact, he soon withdrew himself, taking up the duties of chairman of the Carnegie Institution in Washington. Bush sensed the approach of war, and he had several scientific and industrial ideas that could serve the needs of the armed forces. That is, he wanted to be closer to the center of power, where he could more effectively influence the solution of certain issues.
At the same time, the technical problems dictated by the new design were solved by laboratory staff, and soon they began to be diverted to work on military tasks. The Rockefeller machine was completed only in 1942. The military found it useful for in-line production of ballistic tables for artillery. But soon this device was eclipsed purely digital computers - representing numbers not as physical quantities, but abstractly, with the help of switch positions. It just so happened that the Rockefeller analyzer itself used quite a few of these switches, consisting of relay circuits.
Shannon
In 1936, Claude Shannon was only 20 years old, but he had already graduated from the University of Michigan with a bachelor's degree in two specialties: electrical engineering and mathematics. He was brought to MIT by a flyer pinned to a bulletin board. Vanivar Bush was looking for a new assistant to work on a differential analyzer. Shannon applied without hesitation and soon began to work on fresh problems, and only after that the new device began to take shape.
Shannon didn't look like Bush at all. He was neither a businessman, nor an academic empire builder, nor an administrator. All his life he loved games, puzzles and entertainment: chess, juggling, labyrinths, cryptograms. Like many men of his era, during the war, Shannon devoted himself to a serious cause: he held a position at Bell Labs on a government contract, which protected his fragile body from the military draft. His research on fire control and cryptography during this period led, in turn, to seminal work on information theory (we won't touch on that). In the 1950s, as the war and its aftermath subsided, Shannon returned to teaching at MIT, spending his free time on entertainment: a calculator that worked exclusively with Roman numerals; a machine, when turned on, a mechanical arm appeared from it and turned off the machine.
The structure of the Rockefeller machine that Shannon encountered was logically the same as that of the analyzer of 1931, but it was built from completely different physical components. Bush realized that the rods and mechanical gears in older machines reduced their efficiency: in order to perform calculations, it was necessary to tune the machine, which took many man-hours of work by skilled mechanics.
The new analyzer has lost this shortcoming. At the heart of his design was not a table with rods, but a coordinate switch - an extra prototype donated by Bell Labs. Instead of transmitting power from a central shaft, each integral module was independently driven by an electric motor. To set up the machine to solve a new problem, it was enough just to configure the relays in the coordinate matrix in order to connect the integrators in the desired sequence. A punched tape reader (borrowed from another telecommunications device, a teletype roll) read the configuration of the machine, and a relay circuit converted the signal from the tape into control signals for the matrixβit was like setting up a series of telephone calls between integrators.
The new machine was not only much faster and easier to set up, but also faster and more accurate than its predecessor. She could solve more complex problems. Today, this computer may be considered primitive, even extravagant, but then it seemed to observers to be some great - or perhaps terrible - mind at work:
In fact, it is a mathematical robot. An electrically powered automaton designed not just to take the burden of heavy computation and analysis off the human brain, but also to pounce on and solve math problems beyond mental solution.
Shannon concentrated on converting the data from the paper tape into instructions for the "brain", and the relay circuit was responsible for this operation. He drew attention to the correspondence between the structure of the circuit and the mathematical structures of Boolean algebra, which he studied in his senior year at Michigan. This is an algebra whose operands were TRUE and FALSE, and the operators AND, OR, NOT etc. Algebra, corresponding to logical statements.
After spending the summer of 1937 working at Bell Labs in Manhattan (an ideal place to think about relay circuits), Shannon wrote his master's thesis, A Symbolic Analysis of Relay and Switching Circuits. Along with the work of Alan Turing, written the year before, Shannon's dissertation formed the foundation of the science of computing machines.
In the 1940s and 1950s, Shannon built several computing/logical machines: a THROBAC Roman calculus calculator, a chess endgame machine, and Theseus, a maze driven by an electromechanical mouse (pictured)
Shannon discovered that the system of propositional logic equations could be directly mechanistically translated into a physical circuit of relay switches. He concluded: βIn fact, any operation that can be described in a finite number of steps using words IF, AND, OR etc., can be automatically performed by relays. For example, two controlled switch relays connected in series form a logical Π: current will flow through the main wire only when both electromagnets are activated to close the switches. At the same time, two relays connected in parallel form OR: current flows through the main circuit, activated by one of the electromagnets. The output of such a logic circuit can in turn drive the electromagnets of other relays to produce more complex logic operations like (A Π B) or (C Π D).
Shannon concluded his dissertation with an appendix with several examples of circuits created by his method. Since the operations of Boolean algebra are very similar to arithmetic operations in binary (i.e., using binary numbers), he showed how a relay could be assembled into an "electrical adder in binary" - we call this a binary adder. A few months later, one of the Bell Labs scientists made such an adder on the kitchen table.
Stibitz
George Stibitz, a researcher in the mathematics department at Bell Labs headquarters in Manhattan, brought home a strange set of equipment on a dark November evening in 1937. Dry battery cells, two small light bulbs for hardware shields, and a couple of Type U flat relays found in a trash can. By adding some wires and some junk, he assembled a device that could add two single-digit binary numbers (represented by the presence or absence of input voltage) and output a two-digit number using light bulbs: one - on, zero - off.
Binary Stiebits adder
Stiebitz, a physicist by training, was asked to evaluate the physical properties of relay magnets. Previously, he had no experience with relays at all, and so he began by studying their use in Bell telephone circuits. George soon noticed similarities between some circuits and arithmetic operations with binary numbers. Intrigued, he gathered his side project on the kitchen table.
At first, Stiebitz's relay tinkering aroused little interest among Bell Labs executives. But in 1938, the head of the research group asked George if his calculators could be used for arithmetic operations on complex numbers (for example, a + biWhere i is the square root of a negative number). It turned out that several computing departments at Bell Labs were already moaning at the fact that they constantly had to multiply and divide such numbers. Multiplication of one complex number required four arithmetic operations on a desktop calculator, division - 16 operations. Stiebitz said he could solve the problem and designed a machine for such calculations.
The final design, embodied in metal by telephone engineer Samuel Williams, was called the Complex Number Computerβor Complex Computer for shortβand went into production in 1940. For calculations, 450 relays were used, intermediate results were stored in ten coordinate switches. Data was entered and received using a roll teletype. Bell Labs departments have installed three of these teleprinters, indicating a large demand for computing power. Relays, matrix, teletypes - in every way it was a product of the Bell system.
The finest hour of Complex Computer struck on September 11, 1940. Stiebitz presented a report on the computer at a meeting of the American Mathematical Society at Dartmouth College. He arranged for a teletypewriter to be installed there with a telegraph connection to Complex Computer in Manhattan, 400 kilometers away. Those who wished could walk up to a teletypewriter, enter the conditions of the problem on the keyboard, and see how, in less than a minute, the teletypewriter magically prints the result. Among those who tested the novelty were John Mauchly (John Mauchly) and John von Neumann (John von Neumann), each of whom will play an important role in the continuation of our story.
The meeting participants saw a brief glimpse of the future world. Later, computers became so expensive that administrators could no longer let them sit idle while the user scratched his chin in front of a management console, wondering what to type next. For the next 20 years, scientists will be thinking about how to build general purpose computers that will always be waiting for you to enter data into them, even while working on something else. And then another 20 years will pass until this interactive mode of computing becomes the order of things.
Stiebits at the Dartmouth Interactive Terminal in the 1960s. Dartmouth College was a pioneer in interactive computing. Stiebitz became a college professor in 1964
It is surprising that, despite the tasks it solves, Complex Computer by modern standards is not a computer at all. It could perform complex number arithmetic and probably other similar tasks, but not general purpose ones. It was not programmable. He could not perform operations randomly or repeatedly. It was a calculator capable of doing certain calculations much better than its predecessors.
With the outbreak of World War II, a series of computers named Model II, Model III and Model IV were created at Bell under the leadership of Stibitz (Complex Computer, respectively, was named Model I). Most of them were built at the request of the National Defense Research Committee, and it was headed by none other than Vanevar Bush. Stiebitz improved the layout of the machines in terms of greater function versatility and programmability.
For example, the Ballistic Calculator (later Model III) was developed for the needs of anti-aircraft fire control systems. It was commissioned in 1944 at Fort Bliss, Texas. The device contained 1400 relays and could execute a program of mathematical operations determined by a sequence of instructions on a looped paper tape. A tape with input data was submitted separately, and tabular data separately. This made it possible to quickly find the values ββof, for example, trigonometric functions without real calculations. Bell engineers developed special hunting circuits that scanned the tape forward / backward and looked for the address of the desired table value, regardless of the calculations. Stiebits found that his Model III computer, clicking relays day and night, replaced 25-40 calculators.
Bell Model III Relay Racks
The Model V did not have time to visit the military service. It has become even more versatile and powerful. If measured in terms of the number of computers it replaces, then it was about ten times superior to the Model III. Several computing modules with 9 thousand relays could receive input data from several stations, where users entered the conditions of different tasks. Each such station had one tape reader for data entry and five for instructions. This made it possible to call various subroutines when calculating a task from the main tape. The main control module (in fact, an analogue of the operating system) distributed instructions to the computing modules depending on their availability, and programs could perform conditional jumps. It was no longer just a calculator.
Year of Miracles: 1937
1937 can be considered a turning point in the history of computers. That year, Shannon and Stiebitz noticed similarities between relay circuits and mathematical functions. These findings led Bell Labs to create a series of important digital machines. It was kind of - or even replacement - when a modest telephone relay, without changing its physical form, became the embodiment of abstract mathematics and logic.
In the same year, in the January issue of the publication Proceedings of the London Mathematical Society published an article by the British mathematician Alan Turing "On computable numbers in relation to Β» (On Computable Numbers, With an Application to the Entscheidungsproblem). It described a universal computing machine: the author argued that it could perform actions logically equivalent to those of human calculators. Turing, who had entered graduate school at Princeton University the previous year, was also intrigued by relay circuits. And, like Bush, he is concerned about the growing threat of war with Germany. So he took on a third-party cryptographic project, a binary multiplier that could be used to encrypt military messages. Turing built it from relays made in the university's machine shop.
Also in 1937, Howard Aiken was thinking about a supposed automatic computer. Aiken, a Harvard electrical engineering graduate student, did much of his calculations with nothing more than a mechanical calculator and printed math spreadsheet books. He proposed a design that would get rid of this routine. Unlike existing computing devices, it had to process processes automatically and cyclically, using the results of previous calculations as input for the next ones.
Meanwhile, at the Nippon Electric Company, telecommunications engineer Akira Nakashima had been researching the connections between relay circuits and mathematics since 1935. Finally, in 1938, he independently proved the equivalence of relay circuits to Boolean algebra, which Shannon had discovered a year earlier.
In Berlin, Konrad Zuse, a former aeronautical engineer tired of the endless calculations required at work, was looking for funds to build a second computer. He was unable to get his first mechanical device, the V1, to work reliably, so he wanted to make a relay computer, which he developed with his friend, telecommunications engineer Helmut Schreyer.
The universality of telephone relays, the conclusions about mathematical logic, the desire of bright minds to get rid of stupefying work - all this intertwined and led to the emergence of the idea of ββa new type of logical machine.
forgotten generation
The fruits of the discoveries and developments of 1937 had to ripen for several years. The war proved to be the most powerful fertilizer, and with its advent, relay computers began to appear wherever the necessary technical expertise existed. Mathematical logic has become the vineyard of electrical engineering. New forms of programmable computing machines aroseβthe first draft of modern computers.
In addition to the Stiebitz machines, by 1944 the US could boast the Harvard Mark I/IBM Automatic Sequence Controlled Calculator (ASCC), the result of Aiken's proposal. The double name arose due to the deterioration of relations between the academic environment and industry: everyone laid claim to the device. The Mark I/ASCC used relay control circuits, but the main arithmetic module was built on the IBM mechanical calculator architecture. The machine was created for the needs of the US Bureau of Shipbuilding. Its Mark II successor began working in 1948 at the Navy's test site, and all of its operations were based solely on relays - 13 relays.
Zuse built several relay computers during the war, increasingly complex. The culmination was the V4, which, like the Bell Model V, included setups for calling subroutines and doing conditional jumps. Due to a shortage of materials in Japan, none of Nakashima and his compatriots' designs were embodied in metal until the country had recovered from the war. In the 1950s, the newly formed Ministry of Foreign Trade and Industry funded the creation of two relay machines, the second of which was a monster with 20 relays. Fujitsu, which was involved in the creation, has developed its own commercial products.
Today, these machines are almost completely forgotten. Only one name remains in memory - ENIAC (ENIAC). The reason for forgetting is not related to their complexity, or capabilities, or speed. The computational and logical properties of relays discovered by scientists and researchers apply to any kind of device that can act as a switch. And it so happened that another similar device was available - electronic a switch that could operate hundreds of times faster than a relay.
The importance of World War II in the history of computing machines should already be obvious. The most terrible war was the impetus for the development of electronic machines. Its inception freed up the resources needed to overcome the obvious shortcomings of electronic switches. The dominance of electromechanical computers was short-lived. Like the Titans, they were overthrown by their children. Like relays, electronic switching originated from the needs of the telecommunications industry. And to find out where it came from, we have to rewind our history back to the dawn of the radio age.
Source: habr.com