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From Before the Computer to the Early Days

The development of computers over the last few decades has been very rapid. While there are better sources out there for examining any aspect of the computer revolution in detail, this page provides a very brief overview of some of the major milestones in computing history to provide some historical perspective.


In a section of this site devoted to a homage to the computer front panel, there is some additional material giving detail on some segments of the history of computers. On this page and the one following, drawings of the front panels of the various models in the IBM System/360 range give the history of those computers, and on this page and the one following, the computers of the Digital Equipment Corporation are described and discussed. As well, this page in the section on the computer keyboard discusses the IBM PC and some of its early successors, specifically the IBM PCjr and the IBM PC AT, because each of them brought in a new style of keyboard.

Aids to Calculation

Since the dawn of civilization, people have had to do arithmetic, and it was an irksome and error-prone task.

In Mesopotamia, an early form of the abacus was in use in 2300 BC or earlier; in several cultures, the abacus was in use by 600 to 200 BC.

Napier's first publication describing logarithms and their use as an aid to calculation dates from 1614; William Oughtred invented the slide rule in 1622, which made their use for multiplication to limited precision convenient.

The first mechanical adding machines were invented by Pascal and Schickard in 1642. This type of adding machine is sometimes still seen for sale in grocery stores, in a version made out of plastic; it could only add and subtract. A photograph is shown below:

Gottfried Wilhelm Leibniz, also known for having invented Calculus independently of Newton, and devising the notation for it that we still use today, devised a calculating device known as the "stepped reckoner" which used gears having the form of a cylindrical drum, with nine teeth of different lengths, so that either none of them, or any number from one to nine of them, could be engaged; this allowed multiplication, and Leibniz' mechanism could also divide and take square roots. A drawing of this general type of gear, as used in a more modern calculator, is shown below:

The picture below is of the last surviving specimen of the two prototypes that were originally made, kept in a museum in Hanover; it comes from an old German encyclopedia of mathematics:

Early Automatic Digital Computers

The first attempt at what we think of today as a computer, based on mechanical calculator technology, was, of course, the Analytical Engine by Charles Babbage, first described in 1837, whose portrait is shown at left. The surviving portion of the Difference Engine, which is on display at the South Kensington Museum in London, is shown at right, in an image from The Strand Magazine for June of 1896.

While that project may seem so impractical that it could not have avoided its eventual failure even under more favorable circumstances, the same cannot be said of the later project of his contemporary, Torres y Quevedo, who envisaged building an electrical computer using relays. Torres y Quevedo is best known for the demonstration machine he built to generate interest in, and raise money for, his computer project, a machine that could play a simple Chess endgame, first demonstrated in 1914.

Tabulating equipment using punched cards gradually developed so as to perform some calculating functions. The punched card was invented by Herman Hollerith, who founded a company in 1896 which became the Tabulating Machine Company. This company and three others, the Computing Scale Company of America, the International Time Recording Company, and the Bundy Manufacturing Company, were acquired by Charles R. Flint, and combined to form the Computing-Tabulating-Recording Company in 1911.

Thomas J. Watson succeded to the helm of C-T-R in 1924, and in that year renamed it to International Business Machines. Prior to working for C-T-R, he was a salesman with National Cash Register; it seems obvious to me that his intention in coining the new name for his company was to favorably contrast IBM with NCR; its business is International in scope, not merely National - and it sells every type of Business Machine, not merely Cash Registers!



Analog Computers

In the 1950s and early 1960s, popular works on the computer would often note that there were two fundamental kinds of computer, the digital computer and the analog computer. Today, when we think of computers, we generally only think of digital computers, because they can do all sorts of fun and exciting things.

Analog computers, like slide rules, are limited in the precision of the numbers they work with. They were used to solve complicated equations which would have been too expensive to solve more precisely on the digital computers available at the time.

A famous mechanical analog computer was the Differential Analyzer, constructed by Vannevar Bush starting in 1927. It makes a brief cameo in the movie "When Worlds Collide". One key component involved a wheel that was driven by a rotating disk; as the wheel could be moved do different positions on the disk, changing the effective gear ratio (somewhat the way some automatic transmissions work) it was used to calculate the integral of a function. A famous photograph of Vannevar Bush himself at the Differential Analyzer is shown below:

In the 1950s and early 1960s, electronic analog computers which connected operational amplifiers and other electronic components together with patch cords were commercially available. On the right, an example of such a computer is pictured, the PACE TR20 from EAI, one of the smallest electronic analog computers ever made. It was the successor to their TR10, advertised in 1959 as the first fully-transistorized analog computer.

Pictured below are two analog computers of more typical size, the Packard-Bell TRICE and the EAI Hydac 2000. Both of these are actually hybrid computers, including a digital computer as well as an analog computer, working together for greater versatility.


The Beginnings of the Computer Era

On the left is a photograph of a relay, from an advertisement by Cornell-Dubilier.

At the bottom is a coil, which when energized, acts as an electromagnet, pulling a piece of magnetic material towards one of its poles, causing a lever to move contacts that are at the ends of flexible strips of metal, which we see at the top of the photograph.

Relays, which can obviously act as logic elements, were around for quite some time before computers were built with them, although the idea had occurred to Torres y Quevedo many years before this actually happened.

The Harvard Mark I, conceived in 1939, used a program on a punched paper tape to control calculations performed with electromechanical relays. It became operational in 1944. As initially designed, it did not have a conditional branch instruction. Howard Aiken, its designer, referred to it as "Babbage's dream come true", which shows that Charles Babbage's work did not get rediscovered after the computer age was in full swing, as has occasionally been claimed. The cost of building this computer was largely borne by IBM.

Here is an IBM photograph of this computer:

The ENIAC was the first well-known fully electronic computer. Its completion was announced on February 14, 1946, after having been secretly constructed during World War II. It was originally programmed through plugging patch cords. A classic photograph of it is shown below:

One of its components was an array of dials in which a table of values for a function to be used could be set up; John von Neumann developed a patch cord program that let the machine execute a program entered on those dials. This reduced the speed of the machine's computations, but it drastically shortened the amount of time it took to set the machine up for work on a different problem.

The IBM Selective Sequence Electronic Calculator (SSEC), presented to the public on January 27, 1948, was conceived of as a successor to the Harvard Mark I.

The picture shown above is a detail from an IBM photograph of the SSEC as it appeared on the cover of Naval Research Reviews. Many better pictures of this computer are, of course, available online, but hopefully this will give some idea of how it looked.

It performed calculations electronically on vacuum tubes, but program steps were executed as they were read from special paper tapes.

The paper tapes were the width of 80-column punch cards, and had the same sort of rectangular holes punched in them: however, as the tapes had round sprocket holes on their edges, they were 78-channel tapes.

Numbers used in calculations were retained in three types of storage; the smallest and fastest consisted of vacuum-tube flip-flops; there was also intermediate storage made up of electromechanical relays; and, finally, the same kind of paper tapes used for program steps could also be punched with numbers, and then read back in at several reading stations following the punching station.

Although it was not concieved of, or intended, as a stored-program computer, theoretically program steps could be obtained from the faster forms of storage as well, which has led some to propose that the SSEC rather than the Manchester prototype should be considered the first stored-program computer. It might be asked how this could be possible, since if the SSEC was not designed as a stored-program computer, obviously, it would not have a program counter. However, the instructions of the SSEC each contained the address from which to fetch the next instruction; this was done to facilitate switching to another paper tape reader in order to execute a subroutine or perform a conditional branch, rather than for the reasons this was done on computers with drum memories, but it allowed a program to be put in consecutive locations in fast memory as well.

The SSEC was dedicated to promoting the advance of science. It recieved a considerable amount of publicity in its day, and has been said to have "captured the imagination" of the public. What that meant in practice is that the publicity surrounding the SSEC gave rise to a significantly greater level of public awareness than either the Harvard Mark I or the ENIAC (never mind the Bell Labs relay computer!) that powerful electronic calculating machines existed. Its components, including a console, a dual line printer, and a card reader-punch, were given a gracefully curved design; the wall containing its 12,000 vacuum tubes behind glass panels gave it an imposing appearance. The SSEC itself appeared on the cover of Electronics magazine and Radio Craft, which later became Popular Electronics, but its appearance inspired drawings or paintings of the computer of the future that appeared on the covers of the New Yorker and Astounding Science Fiction, although the latter cover, appearing on the October 1957 issue, also seems to have drawn inspiration from some later machines as well, as the painting includes units resembling the Williams tubes of the IBM 701 computer.

The first problem which it handled was to calculate the position of the Moon for an ephemeris that ran from 1952 through 1959. Incidentally, this means that it is not the case, as occasionally claimed, that its calculations were used in the Apollo missions, as they ran out ten years too soon.

Soon afterwards, many computers were developed that used vacuum tubes to calculate electronically that were much smaller than ENIAC, based on the stored-program concept that John von Neumann had pioneered. Some were still large, like the Univac I, and some were small, like the Bendix G-15.


At right is a photograph, from an advertisement, of a twin-triode tube from Sylvania designed for use in computers, and at left is another photograph, from another advertisement, of a circuit module with vacuum tubes used in the IBM 701 computer. While IBM manufactured its own vacuum tubes for its computers because initially vacuum tube companies were unprepared to meet its demanding standards for reliability, later on Sylvania and General Electric, no doubt among others, produced lines of vacuum tubes specifically designed for use within computers.

Since computers deal in digital signals, while they need high-quality tubes in the area of reliability, they don't require tubes that will amplify signals in a linear fashion with low harmonic distortion. That's why a twin-triode tube is a particularly appropriate type of tube to use for computer logic, as it packs the equivalent of two tubes in the space of one.

Von Neumann himself planned to go on from his work on the ENIAC to create a computer designed around the stored program concept, the EDVAC. As it happened, a British group based at the University of Cambridge was the first to complete a computer based on the EDVAC design, the EDSAC, in May, 1949; the month after, the Manchester Mark I was completed: however, a year before, in June, 1948, the Manchester group had a prototype machine working, giving them the honor of building the world's first stored-program electronic computer.

At first, one of the major problems facing computer designers was finding a way to store programs and data for rapid retrieval at reasonable cost. Recirculating memories, taken from devices originally invented for radar systems, such as mercury delay lines and magnetostrictive delay lines, were used, along with drum memories and their equivalent, head-per-track disks. A special cathode ray tube that stored what was displayed on its face for later readout, called a Williams Tube, provided some of the earliest random-access memories, but it was not as reliable as was desired in practice.

The UNIVAC I and the DEUCE used mercury delay lines, the Bendix G-15, the Royal McBee LGP-30, and the IBM 650 had drum memories, the Ferranti Mercury used magnetostrictive delay lines, and the Maniac I and the IBM 701 used Williams tubes.

The UNIVAC I was the first computer that was offered for sale in a commercial fashion. Before that, organizations with computers either built those computers themselves, or commissioned a company to build them one. Here is a photograph of the Univac I from an advertisement:

The three mercury delay line units are visible through a window in the main cabinets of the computer, directly behind the console typewriter in the image. (Incidentally, it appears that this window was retouched in, as this same photograph appeared in other, earlier, advertisements without that window being present.)

A very similar image of the Univac I, also from an advertisement, but without someone standing by the tape drives (and the person seated at the console was also in a different position) had also been retouched, but under rather different circumstances: that was the one that infamously appeared in the August 23, 1956 issue of Krasnaya Zvesda (Red Star) with the Univac name retouched out as an example of a powerful new Soviet computer! However, the Soviet Union did have early vacuum tube computers, and this may have been more a result of the details of those computers being secret than what would clearly be a pathetically ineffective attempt to fool people into thinking Russia had computers when it didn't.

The first UNIVAC I was installed at the Bureau of the Census for use in tabulating the 1950 census of the United States, on March 31, 1952; this photograph from an announcement of the installation is clearer:

Here, the case doesn't have a window in front of the mercury delay lines, but the door to them has been opened, presumably for cooling.

The magnetic tape drives visible on the right of these images have an unusual characteristic by modern standards; the tape was a ribbon of metal foil, rather than being plastic tape (usually DuPont Mylar®, sometimes polyethylene) with a coating of metal oxide (ussually ferrous oxide, Fe2O3, good old rust, sometimes chromium dioxide, CrO2, with other formulations possible) as was almost universally true since.

The Bendix G-15 computer was relatively inexpensive, and it was used by a number of engineering firms; the company, at one point, celebrated selling their 100th unit of this computer. The IBM 650 was also, at the time, a low-cost computer in IBM's lineup, and one account notes that it was the first computer to be mass-produced, and also the first one to be significantly profitable for IBM.

Below are photographs of the IBM 650 and the Bendix G-15:

Even after core memory became what was used in most computers, for a while recirculating memory was still used even in some computers that used transistors instead of vacuum tubes to allow them to be sold at a low cost. Two examples of this were the Recomp (including the Recomp II and Recomp III) which used a head-per-track disk as main memory, and the Packard-Bell pb250, which used magnetostrictive delay lines.

A photograph of a Recomp II and one of a Packard-Bell pb250 are shown below:

Incidentally, eventually Bendix produced a successor to the G-15, the G-20, illustrated below, that used core memory, and had transistor logic. But that computer still had unusual characteristics.

As can be seen from the image, the G-20 wasn't intended as a direct successor to the G-15, which was a small-scale computer; this new machine was definitely intended as a large-scale mainframe instead.

It had a 32-bit word; a full 32-bit word was called a "logic word", and the computer could add and subtract logic words as well as performing bitwise logical operations on them.

But normally to do integer arithmetic, with multiplication and division included, one used the computer's floating-point facilities. In floating-point numbers, the first two bits of every word were not used; they were always set to zero. This was also true for words containing instructions.

A single-precision float began with 000, and a double-precision float began with 001, so the machine did not need separate double-precision instructions.

There was, however, also a mode bit which could be set to switch the computer into "Pickapoint" mode. In this mode, floating-point numbers changed into fixed-point numbers: the mantissa was extended to the left to also occupy the portion of the number that would have been the exponent. Instead, all numbers had a constant exponent value, which was determined by the contents of the Pickapoint Register.

Thus, this computer had a generalized fixed-point arithmetic capability.

This is quite an unusual machine by modern standards. Wasting two bits of most numbers would not be tolerated these days, of course. Reducing the number of instructions needed by indicating whether a number was single or double precision inside the number may have contributed to the inspiration of the Burroughs machines, but the Burroughs B5000 came out around the same time as it.


The Univac 1103 computer, announced in February 1953, had a 36-bit word, and supplemented a drum memory of 16K words with a random-access Willams Tube memory of 1,024 words. They shared the same address space. The image shown at right is of an 1103 made by Engineering Research Associates before it was acquired by Univac, at the NASA Ames Research Laboratory. The 1103 was succeeded by the Univac 1103A, announced in March, 1956, which also had a drum memory of 16K words, but which used core memory to supplement it; up to three banks of 4,096 words could be used with the computer. Floating-point hardware was available as an option for the Univac 1103A. The 1101, 1102, 1103, and 1103A were also sometimes labelled the Univac Scientific.

Having even a small random-access memory allowed that computer to avoid including a next instruction address in each instruction, and also to largely avoid the need to write programs around when data would be available, while still taking advantage of the fact that drum memory was less expensive.

The magnetic core memory, initially used in the Whirlwind computer prototype, the AN/FSQ-7 computer used for air defense, and the commercial IBM 704 scientific computer, allowed computers to be built which, because they now had dependable memories that were random access in nature, followed the same general model of programming that applied to nearly all computers made subsequently, right up to the present day.


The IBM 704 computer was introduced on May 7, 1954. It is pictured at left. It was the first computer to include both indexing and hardware floating-point as standard features rather than options, and, even more importantly, the first computer sold commercially to have core memory; reliable random-access memory essentially made the IBM 704 one of the first computers to be programmable in the same general manner as we are used to from nearly all later computers; of course, though, even the less-reliable random-access memory of the much less powerful IBM 701 (incidentally, announced on May 21, 1952) also let it be programmed in the same basic manner.

It performed single-precision floating-point arithmetic in hardware; as well, its single-precision floating-point arithmetic instructions retained additional information, normally generated in the course of performing addition, subtraction, or multiplication, that allowed programs to perform double-precision arithmetic to be short and efficient. (This was also true of several other computers that provided single precision, but not double precision, in hardware that came afterwards; the PDP-6 and PDP-10 computers are one example of this, as hardware double precision was not introduced to that architecture until the KI10 chassis for the PDP-10.)

IBM developed the first FORTRAN compiler for the IBM 704. Higher-level languages existed before FORTRAN, but because this compiler was designed to generate highly optimized code, it overcame the major objection to higher-level languages, that they would be wasteful of valuable computer time.

The introduction of FORTRAN for the 704, of course, still further cemented its position as the forerunner of how computers appeared and behaved since that time.

Another historical claim to fame of the IBM 704 was that it was used for the first experimental programs to play both chess and checkers. The chess program, written by Alex Bernstein, had two predecessors that didn't quite qualify; one by Alan Turing which was only executed by hand, and one written for the MANIAC I which played a modified version of chess on a smaller board without Bishops. The checkers program, written by Arther Samuel, had an additional valuable feature; it improved its own play by learning from the results of games it played.

The IBM 704 could have a core memory of 4,096, 8,192, or 32,767 words in size. A drum memory unit with a capacity of 8,192 words of 36 bits was available for the IBM 704 as an optional peripheral device; one or two of them could be attached to the 704.


A successor to the IBM 704 was made, also based on vacuum tubes, the IBM 709, pictured at right. This computer had a considerably expanded instruction set. However, not many of those were made, as it ended up being replaced by the IBM 7090 computer, which had exactly the same instruction set, but which was implemented using transistors. For many years, the IBM 7090 was widely used by those who needed a powerful scientific computer.




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