Identifying the "Early IBM Computer" in a Twitter photo: a 405 Accounting Machine

The photo below of a "woman wiring an early IBM computer" has appeared on Twitter a bunch of times, and it stoked my curiosity: what was the machine in the photo? Was it really an early IBM computer? I was a bit skeptical since the machine in the photo is much smaller than IBM's first room-filling computers, and there aren't any vacuum tubes visible. I investigated this machine and it turned out to be not a computer, but an IBM 405 "Alphabetic Accounting Machine" from 1934, back in the almost forgotten pre-computer age of tabulating machines.1

A common photo on Twitter shows a woman wiring an early IBM computer.

A common photo on Twitter shows a woman wiring an early IBM computer.

The image is from photographer Berenice Abbott who took many scientific photographs from 1939 to 1958. She photographed everything from basic magnetic field and optics experiments to research on early television tubes, and many of these photos were used in physics textbooks. Her photos (including IBM photos) were published in the book Documenting Science. I had hoped that the book would identify the computer in the photo, but it merely said "IBM Laboratory: Wiring an early IBM computer". Surprisingly for an art book, it didn't even give a date for the photo.

The diagram below shows the back view of an IBM 403 accounting machine, which IBM introduced in 1948.2 (An accounting machine (also called a tabulator) summed up and printed records from punched cards for applications such as payroll or inventory.) Note the similarities with the Abbott photo: the thick laced wire bundles, the vertical wire bundles in the middle for the counters, and the hinged doors that swing open.

Back view of an IBM 403 accounting machine. From the IBM 402/403 Field Engineering Manual.

Back view of an IBM 403 accounting machine. From the IBM 402/403 Field Engineering Manual.

A second Berenice Abbott photo shows the machine from a slightly different angle.3 The "Card Feed Circuit Breaker Unit" in the upper right looks like a perfect match between the IBM 403 and the Abbott photo. The dangling cables from the counters in the middle look right, as well as the thick cable between the counters and the circuit breaker unit. The 403 diagram above shows a large printing carriage on top, while the Abbott photo just shows a base, presumably because the carriage hadn't been installed yet.

A second photo of "Woman wiring an early IBM computer" by Berenice Abbott.

A second photo of "Woman wiring an early IBM computer" by Berenice Abbott.

Although the machine in the Abbott photo looks very similar to the IBM 403, there are a few differences if you look carefully. One clear difference is the IBM 403 had caster wheels attached directly to the frame, while the machine in the photos has stubby curved legs. In addition, the doors of the IBM 403 were hinged at a different place. In the Abbott photos, the doors are attached just to the left of the counters and to the right of the card feed circuit breaker unit. But the IBM 403 has some bulky components to the left of the counters such as the "Bijur pump" (an oil pump), and components on the right such as the drive motor. Overall, the machine in the Abbott photos has a narrower cabinet than the IBM 403. Additionally, the thick cable snaking down between the IBM 403's circuit breaker units appears to go straight down in the photos. Thus, although the machine in the photos is very similar to the IBM 403, it's not an exact match.

After more research into IBM's various accounting machines, I conclude that machine in the photos is the IBM 405, an IBM accounting machine introduced in 1934 (earlier than that 1948 IBM 403 despite the larger model number).4 The IBM 405 (below) had curved legs that match the Abbott photos. In addition, the 405 has a narrower main cabinet than the 403, with bulky additional components attached to the left and right, outside the legs. This matches the narrower cabinet in the Abbott photos. (The 403 was an improved and modernized 405, explaining the overall similarity between the two machines.)

An IBM 405 accounting machine. Photo courtesy of Columbia University Computing History.

An IBM 405 accounting machine. Photo courtesy of Columbia University Computing History.

Punched cards were a key part of data processing from 1890 until the 1970s, used for accounting, inventory, payroll and many other tasks. Typically, each 80-column punched card held one record, with data stored in fixed fields on the card. The diagram below shows a typical card with columns divided into fields such as date, vendor number, order number and amount. An accounting machine would process these cards: totaling the amounts, and generating a report with subtotals by account and department, as shown below.

Example of a punched card holding a 'unit record', and a report generated from these cards. The accounting machine can group records based on a field to produce subtotals, intermediate totals, and totals. From Manual of Operation.

Example of a punched card holding a 'unit record', and a report generated from these cards. The accounting machine can group records based on a field to produce subtotals, intermediate totals, and totals. From Manual of Operation.

Punched-card data processing was invented by Herman Hollerith for the 1890 US census, which used a simple tabulating machine to count census data, stored on punched cards. Tabulating machines steadily became more complex, becoming feature-laden "accounting machines" that could generate business reports. Businesses made heavy use of these electromechanical accounting machines and by 1944, IBM had 10,000 tabulating and accounting machines in the field.

Accounting machines were "programmed" with a removable plugboard. By switching the plugboard, an accounting machine could be rapidly reconfigured for different tasks. Each wire corresponded to one character or digit. Wires plugged into the plugboard connected columns on the input card to adders. Each column on the printer had an associated wire controlling what got printed. Other wires had control functions. (I explained the tax preparation plugboard below in detail in this article.)

Plugboard to generate a tax report on an IBM 403 accounting machine. Courtesy of Carl Claunch.

Plugboard to generate a tax report on an IBM 403 accounting machine. Courtesy of Carl Claunch.

The IBM 405 was IBM's first "Alphabetic Accounting Machine," able to print text as well as numbers. It had more complexity than you might expect from the 1930s, able to generate three levels of subtotals, intermediate totals, and grand totals. It could process up to 150 cards per minute; that's remarkably fast for an electromechanical system, reading and summing more than 2 cards per second. The 405 was IBM's flagship product for many years, with IBM manufacturing 1500 of them per year. Like most IBM machines, the 405 was usually rented rather than purchased; it cost over $1000 a month (equivalent to about $15,000 per month in 2017 dollars). Renting out these machines (and selling the punch cards) was highly profitable for IBM, with the IBM 405 accounting machine called "the most lucrative of all IBM's mechanical glories".5

Amazingly, although accounting machines were designed for business purposes, they were also used for scientific computation in the 1930s and 1940s, before digital computers existed. They solved everything from differential equations and astronomy computations to nuclear bomb simulations for the Manhattan Project.6

How does an accounting machine work and what are all those parts?

Accounting machines (also called tabulators) were built from electromechanical components, rather than transistors or even vacuum tubes. The main components in accounting machines were electromechanical counters and relays. Everything was synchronized to rotating driveshafts that ran the counters, card reader and printer. In a way, accounting machines were more like cars than computers, with a motor, clutches, driveshafts, an oil pump, gears and cams.


The heart of the accounting machine was the mechanical counter, a digit wheel somewhat like an odometer. Each wheel stored one digit, with the value indicated by the rotational position of the wheel. To add a number, say 3, to the counter, a clutch was briefly activated, causing the drifeshaft to rotate the counter three more positions. Since these counters were adding 2 1/2 numbers per second, they were spinning rapidly with the clutches engaging and disengaging with precision timing. By combining multiple counters, numbers of up to 8 digits could be handled. The counter kept a running total of the numbers fed into it. Since it accumulated these numbers, the counter was known as an accumulator, a term still used in computing.

A counter unit from an IBM accounting machine. The two wheels held two digits. The electromagnets (white) engaged and disengaged the clutch so the wheel would advance the desired number of positions.

A counter unit from an IBM accounting machine. The two wheels held two digits. The electromagnets (white) engaged and disengaged the clutch so the wheel would advance the desired number of positions.

The photo above shows a board with two counters: the two wheels on the left stored two digits. The counters are more complex than you might expect, with electromechanical circuits to handle carries (including fast carry lookahead). The clutch is underneath the wheel and is engaged by the metal levers in the photo, controlled by electromagnets. A gear underneath the clutch connects the counter to the driveshaft. The electrical connections on the right control the clutch and allow the values from the counters to be read out. Since the IBM 405 had 16 accumulators, with up to 8 digits, many counters were required, resulting in the mass of counter wires in the photos.


Another key component of the accounting machine was the relay, an electromagnetic switch. The control logic of the accounting machine was implemented with hundreds of relays, which would turn on and off to direct the various components of the accounting machine. Example relay functions are switching on when punched cards are in the input hopper, selecting addition or subtraction for a counter, generating the final total when all cards are done, or printing a credit symbol for a negative balance.

The back of the IBM 403 accounting machine shows numerous relays, used to control the machine.

The back of the IBM 403 accounting machine shows numerous relays, used to control the machine.

The relays were mounted on swing-out panels. The photo above shows an IBM 403 with the panels closed. In the Abbott photos the relay panels are opened and you can see the extensive wiring that connected the relays to the rest of the system.

Circuit breakers

The final component I'll explain is the "circuit breaker," which has nothing to do with the circuit breakers in your house. Instead, these are cam-controlled switches that turned on and off (breaking circuits) as the drive shafts rotated. Dozens of circuit breakers provided the timing signals to the accounting machine, ensuring all operations in the machine were synchronized to the drive shaft. (Every 18° of drive shaft rotation corresponded to reading one row on a punched card, moving one character position on a printer typebar, or advancing a counter wheel by one position.)


The woman in Abbott's photos illustrates the large, but mostly ignored role that women played in electrical manufacturing. Women formed the majority of workers in the 1920s radio manufacturing industry, and their presence in electrical manufacturing increased even more when World War II led many women to take industrial jobs. The famous ENIAC computer (1946) also illustrates this: most of the "wiremen" assembling the ENIAC computer were in fact women, probably recruited from the telephone company or radio assembly.8

The photos also provide a glimpse into the era before digital computers, when businesses used electromechanical accounting machines and tabulators for their data processing. Although you'd expect a machine from 1934 to be primitive, the IBM 405 accounting machine in the photos was an advanced piece of technology for its time, containing 55,000 parts and 75 miles of wire.5 These punched card machines were also capable of performing complex scientific tasks, even contributing to the Manhattan Project. In the 1960s, businesses gradually switched from accounting machines to stored-program business computers such as the IBM 1401. Even so, IBM continued marketing accounting machines until 1976.

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Notes and references

  1. By the "era before computers", I mean before digital electronic computers came along in the 1940s. There's a long history of computing machines, analog computers, and human computers (as shown in Hidden Figures) before digital computers came along. Two interesting books that cover this history are The First Computers—History and Architecture or The Computer: From Pascal to von Neumann

  2. IBM's 402 and 403 accounting machines were the same except the 403 could print three-line addresses. This feature was called MLP (multi-line printing) and was useful for printing addresses on invoices, for instance. So when I refer to the IBM 403 accounting machine, I'm also including the IBM 402. 

  3. I was surprised to realize that there are two different, but nearly identical photos of the woman wiring the IBM machine floating around. In first photo, the woman's right leg is straight, there's a screwdriver in front of the bench and she's wiring the left side of the machine. In the second, the woman's left leg is straight and she's wiring the middle of the machine. 

  4. I couldn't find any manuals for the IBM 405 or photos of the back of a 405, so I can't totally nail down the identification. There's a possibility that the Abbott photos show an IBM 401 accounting machine (below), which was similar to the 405 but introduced a year earlier. The IBM 401 and IBM 405 both had the same basic shape and arrangement of components. The main difference is 405 had a full cabinet in front while the 401 was empty in the front with a bar bracing the front feet. The Abbott photos seem to show a full cabinet like the 405, rather than the open 401. Also, since the 405 was a much more popular machine than the 401—the 405 was the "flagship of IBM's product line until after World War II"—the photos are most likely the 405.

    IBM 401 accounting machine (1933). Photo courtesy of Computer History Museum.

    IBM 401 accounting machine (1933). Photo courtesy of Computer History Museum.

  5. Several sources provide information on the IBM 405. One source is Computing before Computers (online) p144. IBM has a FAQ with a short overview. Columbia's Computer History page on the 405 has a longer discussion. Also see IBM's Early Computers, pages 18-22 for information on the IBM 405. Computer: Bit Slices from a Life has some hands-on stories of the IBM 405 (online). Computer: A history of the information machine page 51 has some information on the IBM 405. 

  6. See Punched Card Methods in Scientific Computation, 1940 for details on how accounting machines were used for scientific computation. The book is by W. J. Eckert, confusingly unrelated to the ENIAC's J. Presper Eckert. The use of IBM accounting machine by the Manhattan Project is described by Feynman in Los Alamos from Below, p25; and in this page. The Manhattan Project used a 402 accounting machine, several IBM 601 multiplying punches for multiplication, and other card equipment (reference, with more details in Early Computing at Los Alamos). 

  7. Bitsavers has manuals for the later 402/403 accounting machines. The operation of accounting machines is discussed in detail in IBM 402, 403 and 419 Accounting Machines: Manual of Operation. For a thorough discussion of how the machine works internally, see IBM 402, 403, 419 Field Engineering Manual of Instruction. For an overview of how plugboard wiring for IBM's works, see IBM Functional Wiring Principles

  8. Women and Electrical and Electronics Manufacturing provides a detailed discussion of the history of women in technological manufacturing in the 20th century. The book ENIAC in Action describes how most of the wiring of the ENIAC was done by women. It also has a detailed discussion of the role of women as programmers for early computers such as the ENIAC. 


Grumpy said...

I still have an original plugboard. I got it from IBM as a thanks for a service provided.

Pierre Clouthier said...

I arrived at my first job in 1970 to see the IBM 403 Tabulator being hauled away. There was an oilpan under the machine.

I did wire a panel for a Univac 1001 high-speed card reader (2,000 cards/min.)

Unknown said...

I see a Bijur pump in one pic that is an oiler that pumps a couple times per hour, depending how it's set.

Bayan Nazaaha Shamoon said...

thank u

gavineadie said...

I mentioned this article to some retired University of Michigan Computing Center buddies and all reminisced !

In particular, "I’m surprised the article didn’t mention the 407 in an otherwise fairly complete overview of IBM 40x machines. I think the 407 was the last machine of that sort IBM made and was their flagship for quite a long time. There’s a good Wikipedia article about it at Tom McBride and I spent quite a lot of time wiring one of these for a job we had briefly in Houston. They were more complex than you might think and with a little bit of imagination you could make them do a lot."

Ken Shirriff said...

Thanks for the info gavineadie. I didn't intend for the article to be an overview of all the accounting machines. Since the 407 clearly wasn't the machine in the photo, I left it out of the discussion. It is an interesting machine, though.

Jim Cortada said...

By intro, I am a retired IBMer. Excellent piece of analysis by you. When I lived in Poughkeepsie, NY in the early 1980s I was told by neighbors that IBM used women to wire computers in the 1950s through the 1960s, because they paid more attention to details then men, and many knew how to knit (e.g., older women).

Unknown said...

My father began working for IBM in 1927. Later will tell where. I started in IBM in 1957. Both of us were "Customer engineers" (repairmen) . My father was Manager of the service division. We worked on 405'S, 420'S and 421'S, all accounting machines. Also 602A: this was a calculator. By 1962 I learned programming for the 1401 series, and worked as coder at first and in almost all duties related to computers (360, 370, 390) until 2011.
Father started working in Buenos Aires and me in Montevideo. The pictures broght memories I wanted to share. (English,obviously, not my mother tonguer!)

ZERIMAR said...

Congratulations on the blog because it really represents what the beginning of computing was. In 1956 I started working with the unit record equipment. I had the privilege of teaching for several years and teaching hundreds of people to operate and program these equipment. The IBM equipment that was available in the 50s was essential for the advancement of computing. In that decade the IBM 650 appeared that it was already a real computer with a stored program, which after all was the concept that changed the way of doing things. Already in the decade of the 60's, 1401, 1440 and 1410 appeared that even being stored program computers they conserved the technologies of the Unit Record to address the solutions of systems of all kinds. The IBM 1620 also appeared to solve scientific problems. But things were going very fast and these devices were barely installed and began to be used when the IBM 360 was announced in 1964, although the first installations were made in 1966. It was an interesting and heroic era in a way, because it had to put a lot of talent in solving problems with tools that appeared to us as very advanced when in reality they were not. An IBM 1401 had an average of 4k of RAM and a thousand things had to be invented to work with these limitations. Today the RAM of any pc is 4GB, that is a million times larger

David Beaumont said...

While going through my wife’s grandmother‘s belongings after her passing in 1999 (the grandmother), we came across two business sized cards, one from IBM, the other from the War Department. I’d forgotten about them until this morning and decided to google and see if there was anything available that might provide some insight as to what they were for.

The IBM card was a certification that she passed the “407 Wiring” course in May 1953 with a final grade of “A”. I have always wondered what a 407 was and what the course about. Thanks to your article, this mystery is solved and we now have a little bit of history to share with my wife’s family. Thanks so much.

I still don’t know what the war dept “Job Methods Training” certification card was for, but suspect it was related to the IBM 407 training in some way.

BTW. I retired from IBM in 2014.