The IBM 610 Auto-Point Computer

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Thewas designed in the portholed attic of Watson Lab at Columbia University by John Lentz between 1948 and 1954 as the Personal Automatic Computer (PAC) and announced by IBM as the 610 Auto-Point in 1957[ 1 ]. The IBM 610 was thein the sense that it was the first computer intended for use by one person (e.g. in an office) and controlled from a keyboard[ 2 ]. The large cabinet contains a magnetic drum, the arithmetic control circuitry, a control panel , and separate paper-tape readers and punches for program and data (according to one former user, Russ Jensen , "The machine was programmed by a punched paper tape which duplicated itself in order to perform extra passes through the code". The IBM electric typewriter printed the output at 18 characters per second; the other device was the operator's keyboard for control and data entry, which incorporated a small cathode ray tube (two inches, 32×10 pixels) that could display the contents of any register [ 4 ]. A "register" is any of 84 drum locations (31 digits plus sign). The control panel provides additional programming control (e.g. for creating subroutines, typically for trigonometric or other mathematical functions). Price: $55,000.00 (or rental at $1150/month, $460 academic). 180 units were produced.

Lentz said of the 610, "A novel approach to com­puter pro­gram­ming and control, used in the IBM 610 computer, allows the solution of complex problems by an operator whose only previous experience with computing has been the desk calculator. The machine's command structure is designed so that the operator can at all times communicate with the computer by a series of short sentence-type instructions closely resembling the steps of manual arithmetic solution. A type of floating-decimal operation called the 'auto-point' mode permits entry of data into storage locations with automatic positioning of the decimal point, without elaborate programming. The decimal point is automatically re-positioned during subsequent computation" (Reference 1).

Users said (Reference 2) the machine was affordable, reliable (95% uptime was typical), easy to program (it was one of the first — if not the first — computer that was programmable symbolically from a keyboard), handled floating-point arithmetic naturally, and did not require air conditioning or special power. Some, however, faulted it for its execution speed (e.g. 20 seconds to calculate a sine). But as Brennan says, "Far ahead of its time conceptually, the 610 presaged 'on-line' direct communication between individual and computer." When the 610 was discontinued (it was technologically obsolete from the start, due to the long delay in getting it to market), most sites replaced it with a 1620.

IBM produced several other personal computers in later years, including the 5100 and the CS-9000 before finally releasing its world-conquering PC in 1981 (the CS-9000 was ready before the PC but announced after it).

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Brennan [9] says the first 610 prototype was "completed at Watson Lab in 1948". Grosch [59] says "Lentz's 610 did not exist even in prototype when I left in 1951 —- if 'under wraps', the wrapping was much later." According to Bashe [4], the first engineering model of the Auto-Point Computer was operational in 1954, but release was delayed by IBM's rollout of its 650 and 700-series computers. The 610 was IBM's second-to-last vacuum tube computer. Sometimes the refrigerator-size Bendix G-15 (1956) is called the "first personal computer", but the 610 was running at least two years earlier. In any case the 610 was intended to be personal, whereas the G-15 was intended to be inexpensive [59].) (Another device sometimes named the first personal computer is Simon — also associated with Columbia University! — but it was a limited-function demonstration device.

For reasons lost in time, the construction of the first prototypes was farmed out to Burroughs/ElectroData in Pasadena, CA, which also made contributions to the design. In May 2004, I received the following comments from John C. Alrich, who was on the 610 design team at Burroughs, and worked with Lentz for 12-18 months in Pasadena on the project:

I was on the design team from Burroughs. In fact, I had a patent on part of the drum design. John was indeed the architect but Burroughs, Pasadena, played no small part in the design and building of several of the prototypes. The only printed data I have from that project is my patent which was filled 4/14/55 and issued 9/17/57, so April '55 must have been in the middle of our design phase in Pasadena. I have no other documents. I do remember Herb Grosch coming out and looking at the machine when it was well along [John, with Jack Palmer, also of IBM, had been up half the night getting the square root function to work for this demo; the 610 was the first IBM product with built-in square root capability*. I don't remember whether we were part of Burroughs yet or still a subsidiary of Consolidated Electrodynamics Corporation, called ElectroData. CEC manufactured mass spectrometers and our first computer was designed to invert large matrices that were used in compound analysis. The guy that pushed CEC into the computer business was Clifford Berry, who designed mass spectrometers, and who — are you ready for this — got his Ph.D. under Atanasoff before World War II and worked with Atanasoff on his first computer there at the University! Cliff did not work on our first computer, called the Datatron 201, but continued with designing mass spectromters. I think Cliff died in the late fifties at an early age. John's design was radically different from the CEC/von Neumann design I was familiar with in that the circuitry was dynamic rather than static; i.e. he used free-running multivibrators rather than static flip-flops for his logic. He did not think ff's were stable! I can go into more of that later. The other strange thing in the design (to me at least) was that the 610 was essentially a Turing machine; i.e., in principle, it had infinite capacity for input data and for intermediate and final output data. The means, of course, was punched paper tape, both working, as I recall, at 18 characters/second! The small plated drum was also used to store intermediate results. John used lots of wire relays in his design too. Why I was assigned to the project by L.P. Robinson (Robbie), I'll never know. I was not a circuit person although, from 1951-52 I worked under a brilliant mathematician, Ernst Selmer, who was the #2 mathematician in Norway and was working with von Neumann's group before he came west to teach at Cal Tech for a year or so. So I knew logic design pretty well (I designed the Floating Point Control for the Datatron in 1957, the most satisfactory piece of design I did in a career of 40 years). It was interesting to read that IBM made 180 units, about which I have only two comments: Because of the dynamic circuitry, if the clock lost synchronization, you couldn't hold a fixed image on a 'scope screen to do any debugging; and When this happened, Lentz was one of the few people in the world who could analyze the trouble and fix it. I wonder how IBM's Field Service managed? On re-thinking about the 610, I still find it an enigma. There were a lot of clever ideas in it, mostly John's, but I think John went up the wrong limb of the computer evolution tree. In principle, his machine could solve any mathematics problem that could be solved in finite time but by using relay trees and paper-tape I/O, the speed of execution was intolerably slow, even by 1955 standards.

The photos in this section are from John Lentz's article on the 610 ( Reference 1 below); click on an image to get a bigger version. The top figure shows the computer opened up to reveal its insides. The cabinet at left contains the electronic arithmetic unit with its magnetic drum storage unit and electromechanical controls, with paper tape input/output on top. On the desk is an electric typewriter for printed output and a "manual control keyboard which provides a cathod-ray tube display in coded form of the content of any desired machine register" (center figure). The complete system weighs 750 pounds and and draws less than 20 amps from a single 120-volt circuit. The control panel (bottom figure) can be used to program commonly used functions such as sine or cosine, so they don't have to be read repeatedly from the control tape.

John Alrich comments (June 2004): "In many ways the 610 was unique or nearly unique for its day or any other day. One attribute in particular was the method of numerical encoding. As I recall, each word was fifteen digits long using pulse position encoding. That is, each of the fifteen digits was twelve serial slots long. Depending upon where a pulse or pulses appeared within each digit determined the value of that digit, the sign of the word and the decimal location. Therefore the serial display was rather simple — a CRT with a single modulated beam. A transparent engraved reticle, with 180 small slots, placed in front of the CRT allowed the user to read out immediately the numeric value of the word being displayed.

"I think with pulse-position modulation it becomes fairly obvious how certain arithmetic operations are performed. Since the 610 was non-Boolean, arithmetic operations were generally done by counting rather than with Boolean logic. Using the drum for temporary storage, during an add, for example, the addend and the augend are simultaneously available in serial form. The add operation probably was done something like the following: The addend and the augend were read off the drum in synchronization serially, least significant digit first. In between clocks on the drum (enclosing a full word), each digit of the augend was counted down at a high rate to zero while each digit of the addend was counted up, with carry noted for inclusion while counting the next digit. In this way the sum was determined within one word time of the drum revolution. Subtraction could be performed in a similiar way replacing the carry with a borrow; multiplication, division and square-root were, of course, more complex."

John relates that the people at Burroughs called the 610 the CADET ("Can't Add, Doesn't Even Try"), the same term used by IBMers for the 1620. For more about John's experiences at Burroughs see:



The IBM 610 saw widespread use in the military and academia for scientific applications. These photos are from the US Army Ballistics Research Lab (BRL), Aberdeen Proving Ground, Maryland, about 1961, where the 610 was used for heat transfer calculations, analysis of mass spectrometric data, formulae evaluations, calculation of aeroelasticity, stress analysis, flutter and vibration analysis, data reduction, highway design, bridge design, surveying problems, matrix arithmetic, correlation and regression analysis, sales forecasting, actuarial calculations, analysis of variance, curve fitting, experimental design, and many other applications. Installations included BRL, the US Army Transportation Research Command; the US Naval Academy; the US Naval Ammunition Depot QE Laboratory; White Sands Missile Range; the Tennessee Valley Authority; DuPont ; General Tire and Rubber; Lockheed Aircraft; Carlton College; the University of Louisville; the University of Rhode Island; the University of Waterloo , Worcester Polytechic Institute, and of course Columbia University, where it was used for work in physical chemistry until about 1965. Military sites often had 3 or 4 each; it could be put on a truck and taken to the field, and it could also be put on an aircraft.

Photos: From Reference 2, scanned by Ed Thelen. Click on images to enlarge.