Bendix G-15

The Bendix G-15 computer was introduced in 1956[1][2][3] by the Bendix Corporation, Computer Division, Los Angeles, California. It is about 5 by 3 by 3 ft (1.5m by 1m by 1m) and weighs about 966 pounds (438 kg).[4][5] The base system, without peripherals, cost $49,500. A working model cost around $60,000 (over $500,000 by today's standards). It could also be rented for $1,485 per month. It was meant for scientific and industrial markets. The series was gradually discontinued when Control Data Corporation took over the Bendix computer division in 1963.

The chief designer of the G-15 was Harry Huskey, who had worked with Alan Turing on the ACE in the United Kingdom and on the SWAC in the 1950s. He made most of the design while working as a professor at Berkeley, and other universities. David C. Evans was one of the Bendix engineers on the G-15 project. He would later become famous for his work in computer graphics and for starting up Evans & Sutherland with Ivan Sutherland.

Bendix G-15
Bendix G-15, 1956
DeveloperHarry Huskey
ManufacturerBendix Corporation
Release date1956
Introductory priceUS$49,500 (Base system without peripherals)
Units sold400
Dimensions5 by 3 by 3 ft (1.5m by 1m by 1m)
Massabout 966 pounds (438 kg)
Bendix G-15 computer, 2015


The G-15 was inspired by the Automatic Computing Engine (ACE). It is a serial-architecture machine, in which the main memory is a magnetic drum. It uses the drum as a recirculating delay line memory, in contrast to the analog delay line implementation in other serial designs. Each track has a set of read and write heads; as soon as a bit was read off a track, it is re-written on the same track a certain distance away. The length of delay, and thus the number of words on a track, is determined by the spacing of the read and write heads, the delay corresponding to the time required for a section of the drum to travel from the write head to the corresponding read head. Under normal operation, data are written back without change, but this data flow can be intercepted at any time, allowing the machine to update sections of a track as needed.

This arrangement allowed the designers to create "delay lines" of any desired length. In addition to the twenty "long lines" of 108 words each, there are four more short lines of four words each. These short lines recycle at 27 times the rate of the long lines, allowing fast access to frequently needed data. Even the machine's accumulators are implemented as drum lines: three double-word lines are used for intermediate storage and double-precision addition, multiplication, and division in addition to a one single-word accumulator. This use of the drum rather than flip-flops for the registers helped to reduce vacuum tube count.

A consequence of this design was that, unlike other computers with magnetic drums, the G-15 does not retain its memory when it is shut off. The only permanent tracks are two timing tracks recorded on the drum at the factory. The second track is a backup, as the tracks are liable to erasure if one of their amplifier tubes shorted out.

The serial nature of the G-15's memory was carried over into the design of its arithmetic and control circuits. The adders work on one binary digit at a time, and even the instruction word was designed to minimize the number of bits in an instruction that needed to be retained in flip-flops (to the extent of leveraging another one-word drum line used exclusively for generating address timing signals).

The G-15 has 180 vacuum tube packs and 300 germanium diodes.[6] It has a total of about 450 tubes (mostly dual triodes).[7] Its magnetic drum memory holds 2,160 words of twenty-nine bits. Average memory access time is 14.5 milliseconds, but its instruction addressing architecture can reduce this dramatically for well-written programs. Its addition time is 270 microseconds (not counting memory access time). Single-precision multiplication took 2,439 microseconds and double-precision multiplication take 16,700 microseconds.


One of the G-15's primary output devices is the typewriter with an output speed of about 10 characters per second for numbers (and lower-case hexadecimal characters u-z) and about three characters per second for alphabetical characters. The machine's limited storage precludes much output of anything but numbers; occasionally, paper forms with pre-printed fields or labels were inserted into the typewriter. A faster typewriter unit was also available.

The high-speed photoelectric paper tape reader (250 hexadecimal digits per second on five-channel paper tape for the PR-1; 400 characters from 5-8 channel tape for the PR-2) read programs (and occasionally saved data) from tapes that were often mounted in cartridges for easy loading and unloading. Not unlike magnetic tape, the paper tape data are blocked into runs of 108 words or less since that is the maximum read size. A cartridge can contain many multiple blocks, up to 2500 words (~10 kilobytes).

While there is an optional high-speed paper tape punch (the PTP-1 at 60 digits per second) for output, the standard punch operates at 17 hex characters per second (510 bytes per minute).

Optionally, the AN-1 "Universal Code Accessory" included the "35-4" Friden Flexowriter and HSR-8 paper tape reader and HSP-8 paper tape punch. The mechanical reader and punch can process paper tapes up to eight channels wide at 110 characters per second.

The CA-1 "Punched Card Coupler" can connect one or two IBM 026 card punches (which were more often used as manual devices) to read cards at 17 columns per second (ca. 12 full cards per minute) or punch cards at 11 columns per second (ca. eight full cards per minute). Partially full cards were processed more quickly with an 80 column per second skip speed). The more expensive CA-2 Punched Card Coupler reads and punches cards at a 100 card per minute rate.

The PA-3 pen plotter runs at one inch per second with 200 increments per inch on a paper roll one foot wide by 100 feet long. The optional retractable pen-holder eliminates "retrace lines".

The MTA-2 can interface up to four drives for half-inch Mylar magnetic tapes, which can store as many as 300,000 words (in blocks no longer than 108 words). The read/write rate is 430 hexadecimal digits per second; the bidirectional search speed is 2500 characters per second.

The DA-1 differential analyzer facilitates solution of differential equations. It contains 108 integrators and 108 constant multipliers, sporting 34 updates per second.


A problem peculiar to machines with serial memory is the latency of the storage medium: Instructions and data are not always immediately available and, in the worst case, one must wait for the complete recirculation of a delay line to obtain data from a given memory address. The problem is addressed in the G-15 by what the Bendix literature calls "minimum-access coding." Each instruction carries with it the address of the next instruction to be executed, allowing the programmer to arrange instructions such that when one instruction completes, the next instruction is about to appear under the read head for its line. Data can be staggered in a similar manner. To aid this process, the coding sheets include a table containing numbers of all addresses; the programmer can cross off each address as it is used.

A symbolic assembler, similar to the IBM 650's SOAP (Symbolic Optimal Assembly Program), was introduced in the late 1950s and includes routines for minimum-access coding. Other programming aids include a supervisor program, a floating-point interpretive system named "Intercom", and ALGO, an algebraic language designed from the 1958 Preliminary Report of the ALGOL committee. Users also developed their own tools, and a variant of Intercom suited to the needs of civil engineers is said to have circulated.

Floating point is implemented in software. The "Intercom" series of languages provide an easier to program virtual machine that operates in floating point. Instructions to Intercom 500, 550, and 1000 are numerical, six or seven digits in length. Instructions are stored sequentially; the beauty is convenience, not speed. Intercom 1000 even has an optional double-precision version.

As mentioned above the machine uses hexadecimal numbers. But the user never has to deal with this in normal programming. The user programs use the decimal numbers while the OS resides in the higher addresses.


The G-15 is sometimes described as the first personal computer, because it has the Intercom interpretive system. The title is disputed by other machines, such as the LINC and the PDP-8, and some maintain that only microcomputers, such as those which appeared in the 1970s, can be called personal computers. Nevertheless, the machine's low acquisition and operating costs, and the fact that it does not require a dedicated operator, meant that organizations could allow users complete access to the machine.

Over 400 G-15s were manufactured. About 300 G-15s were installed in the United States and a few were sold in other countries such as Australia and Canada. The machine found a niche in civil engineering, where it was used to solve cut and fill problems. Some have survived and have made their way to computer museums or science and technology museums around the world.

Huskey received one of the last production G15s, fitted with a gold-plated front panel.

This was the first computer that Ken Thompson ever used.[8]

See also


  1. ^ Grieco, Joseph M. (1984). Between Dependency and Autonomy: India's Experience with the International Computer Industry. University of California Press. p. 57. ISBN 9780520048195.
  2. ^
  3. ^
  4. ^ (850 + 965 + 1050 + 1000) / 4 = 966.25 850 lbs:
    965 lbs, 1050 lbs:
    • "Index of /pdf/bendix/g-15". T10-3_G15_Tech_Bulletin_Apr60.pdf, p. 16; JH-039_G-15_Installation_Mar59.pdf, p. 4. Retrieved 2018-06-08.
    1000 lbs:
    • Weik, 1961
  5. ^ Weik 1961.
  6. ^ "The Bendix G-15"
  7. ^ Weik, Martin H. (1961). "BENDIX G 15". A Third Survey of Domestic Electronic Digital Computing Systems.
  8. ^ "Coders At Work", chapter 12: "Ken Thompson", page 494 by Peter Seibel, 2009

External links


ALGO is an algebraic programming language developed between 1959 and 1961 for the Bendix G-15 computer.

ALGO was one of several programming languages inspired by the Preliminary Report on the International Algorithmic Language written in Zürich in 1958. This report underwent several modifications before becoming the Revised Report on which most ALGOL implementations are based. As a result, ALGO and other early "ALGOLs" have a very different syntax from ALGOL 60.

Other languages


ALGOL 58, originally known as IAL, is one of the family of ALGOL computer programming languages. It was an early compromise design soon superseded by ALGOL 60. According to John Backus

"The Zurich ACM-GAMM Conference had two principal motives in proposing the IAL: (a) To provide a means of communicating numerical methods and other procedures between people, and (b) To provide a means of realizing a stated process on a variety of machines..."

ALGOL 58 introduced the fundamental notion of the compound statement, but it was restricted to control flow only, and it was not tied to identifier scope in the way that Algol 60's blocks were.

Alan Turing

Alan Mathison Turing (; 23 June 1912 – 7 June 1954) was an English mathematician, computer scientist, logician, cryptanalyst, philosopher and theoretical biologist. Turing was highly influential in the development of theoretical computer science, providing a formalisation of the concepts of algorithm and computation with the Turing machine, which can be considered a model of a general-purpose computer. Turing is widely considered to be the father of theoretical computer science and artificial intelligence. Despite these accomplishments, he was never fully recognised in his home country during his lifetime, due to his homosexuality, which was then a crime in the UK.

During the Second World War, Turing worked for the Government Code and Cypher School (GC&CS) at Bletchley Park, Britain's codebreaking centre that produced Ultra intelligence. For a time he led Hut 8, the section that was responsible for German naval cryptanalysis. Here, he devised a number of techniques for speeding the breaking of German ciphers, including improvements to the pre-war Polish bombe method, an electromechanical machine that could find settings for the Enigma machine.

Turing played a pivotal role in cracking intercepted coded messages that enabled the Allies to defeat the Nazis in many crucial engagements, including the Battle of the Atlantic, and in so doing helped win the war. Counterfactual history is difficult with respect to the effect Ultra intelligence had on the length of the war, but at the upper end it has been estimated that this work shortened the war in Europe by more than two years and saved over 14 million lives.After the war, Turing worked at the National Physical Laboratory, where he designed the Automatic Computing Engine, which was one of the first designs for a stored-program computer. In 1948, Turing joined Max Newman's Computing Machine Laboratory at the Victoria University of Manchester, where he helped develop the Manchester computers and became interested in mathematical biology. He wrote a paper on the chemical basis of morphogenesis and predicted oscillating chemical reactions such as the Belousov–Zhabotinsky reaction, first observed in the 1960s.

Turing was prosecuted in 1952 for homosexual acts; the Labouchere Amendment had mandated that "gross indecency" was a criminal offence in the UK. He accepted chemical castration treatment, with DES, as an alternative to prison. Turing died in 1954, 16 days before his 42nd birthday, from cyanide poisoning. An inquest determined his death as a suicide, but it has been noted that the known evidence is also consistent with accidental poisoning.In 2009, following an Internet campaign, British Prime Minister Gordon Brown made an official public apology on behalf of the British government for "the appalling way he was treated". Queen Elizabeth II granted Turing a posthumous pardon in 2013. The Alan Turing law is now an informal term for a 2017 law in the United Kingdom that retroactively pardoned men cautioned or convicted under historical legislation that outlawed homosexual acts.

Bendix Corporation

The Bendix Corporation was an American manufacturing and engineering company which during various times in its 60-year existence (1924–1983) made automotive brake shoes and systems, vacuum tubes, aircraft brakes, aeronautical hydraulics and electric power systems, avionics, aircraft and automobile fuel control systems, radios, televisions and computers. It was also well known for the name Bendix, as used on home clothes washing machines, but never actually made these appliances.

Colossus computer

Colossus was a set of computers developed by British codebreakers in the years 1943–1945 to help in the cryptanalysis of the Lorenz cipher. Colossus used thermionic valves (vacuum tubes) to perform Boolean and counting operations. Colossus is thus regarded as the world's first programmable, electronic, digital computer, although it was programmed by switches and plugs and not by a stored program.Colossus was designed by research telephone engineer Tommy Flowers to solve a problem posed by mathematician Max Newman at the Government Code and Cypher School (GC&CS) at Bletchley Park. Alan Turing's use of probability in cryptanalysis (see Banburismus) contributed to its design. It has sometimes been erroneously stated that Turing designed Colossus to aid the cryptanalysis of the Enigma. Turing's machine that helped decode Enigma was the electromechanical Bombe, not Colossus.The prototype, Colossus Mark 1, was shown to be working in December 1943 and was in use at Bletchley Park by early 1944. An improved Colossus Mark 2 that used shift registers to quintuple the processing speed, first worked on 1 June 1944, just in time for the Normandy landings on D-Day. Ten Colossi were in use by the end of the war and an eleventh was being commissioned. Bletchley Park's use of these machines allowed the Allies to obtain a vast amount of high-level military intelligence from intercepted radiotelegraphy messages between the German High Command (OKW) and their army commands throughout occupied Europe.

The existence of the Colossus machines was kept secret until the mid-1970s; the machines and the plans for building them had previously been destroyed in the 1960s as part of the effort to maintain the secrecy of the project. This deprived most of those involved with Colossus of the credit for pioneering electronic digital computing during their lifetimes. A functioning rebuild of a Mark 2 Colossus was completed in 2008 by Tony Sale and some volunteers; it is on display at The National Museum of Computing at Bletchley Park.

David C. Evans

David Cannon Evans (February 24, 1924 – October 3, 1998) was the founder of the computer science department at the University of Utah and co-founder (with Ivan Sutherland) of Evans & Sutherland, a computer firm which is known as a pioneer in the domain of computer-generated imagery.


In mathematics and computing, hexadecimal (also base 16, or hex) is a positional numeral system with a radix, or base, of 16. It uses sixteen distinct symbols, most often the symbols "0"–"9" to represent values zero to nine, and "A"–"F" (or alternatively "a"–"f") to represent values ten to fifteen.

Hexadecimal numerals are widely used by computer system designers and programmers, as they provide a more human-friendly representation of binary-coded values. Each hexadecimal digit represents four binary digits, also known as a nibble, which is half a byte. For example, a single byte can have values ranging from 0000 0000 to 1111 1111 in binary form, which can be more conveniently represented as 00 to FF in hexadecimal.

In mathematics, a subscript is typically used to specify the radix. For example the decimal value 10,995 would be expressed in hexadecimal as 2AF316. In programming, a number of notations are used to support hexadecimal representation, usually involving a prefix or suffix. The prefix 0x is used in C and related languages, which would denote this value by 0x2AF3.

Hexadecimal is used in the transfer encoding Base16, in which each byte of the plaintext is broken into two 4-bit values and represented by two hexadecimal digits.

Hurricane Supersonic Research Site

The Hurricane Supersonic Research Site (HSRS) was formerly on Hurricane Mesa in Washington County, Utah. It was a United States Air Force (USAF) launch complex with a rocket research track that launched a rocket ejection seat from a supersonic sled.

The track's 12,000 ft (3,700 m) "of continuously welded, heavy-duty crane-rails aligned to within plus or minus one-tenth inch tolerance [was] the longest" in the US (cf. the shorter 1954 Holloman Rocket Sled). Coleman Engineering Company was contracted for $2 million in June 1954 and constructed the Supersonic Military Air Research Track (SMART), mechanical arresting gear (water brakes with 34 tons of force), retro rockets, and photographic/telemetering facilities. Coleman was also contracted for operations on November 30, 1955, and achieved a "world land speed record [using] a 9,400-pound sled rocketing down the track at 1,800 miles per hour." The numerous test facilities included a powered comparator for high-speed motion pictures, a 1956 IBM 706 computer, and 1960 Bendix G-15 computer. Control of the site transferred from Indian Springs Air Force Base on November 6, 1957, and from Wright-Patterson AFB to Edwards AFB on March 9, 1962—the base was placed on standby in December 1961, and was closed on June 20, 1963.The 3,500.78-acre (1,416.72 ha) Formerly Used Defense Site (J08UT0026) initially transferred to Stanley Aviation and was leased to Sacol, Inc. on May 21, 1965.Adjacent to the Hurricane Mesa Airport (37°14′59″N 113°12′31″W), the privately owned Hurricane Mesa Test Facility is owned and managed by the Collins Aerospace division of the United Technologies Corporation.

List of pioneers in computer science

This article presents a list of individuals who made transformative breakthroughs in the creation, development and imagining of what computers and electronics could do.

Magnetic Drum Digital Differential Analyzer

The MADDIDA (MAgnetic Drum DIgital Differential Analyzer) was a special-purpose digital computer used for solving systems of ordinary differential equations. It was the first computer to represent bits using voltage levels and whose entire logic was specified in Boolean algebra.

Invented by Floyd Steele, MADIDDA was developed at Northrop Aircraft Corporation between 1946-49 to be used as a guidance system for the Snark missile. No guidance system, however, resulted from the work on the MADDIDA, and rather it was used for aeronautical research In 1952, the MADDIDA became the world's top-selling commercial digital computer (albeit a special-purpose machine), six units having been sold. (The general-purpose UNIVAC I delivered its seventh unit in 1954.)

Optimum programming

In the history of computing, optimum programming, or optimum coding is the practice of arranging a computer program's instructions in memory so as to minimize the time the machine spends waiting for instructions. It is of historical interest mainly due to the design of many early digital computers.

Most early computers used some form of serial memory, primarily delay line memory or magnetic drums Unlike the random access memory of modern computers, words in serial memory are made available one at a time; the time required to access a particular word depends on the "distance" between it and the word currently being read. If a given delay line held n words, the average time to read a word would be word times. Without optimum coding, such a machine would spend most of its time idly waiting for instructions and data.

To circumvent this problem, many machines, particularly Alan Turing's ACE and its descendants, included a field specifying the address of the next instruction to be executed in their instruction format. A programmer employing optimum coding would look up the time needed to perform the current instruction, calculate how far the memory system would move in that time, and then place the next instruction for the program at that location. Thus when the current instruction completed and the computer looked for the next one as specified in the instruction, that memory location would just be arriving and would be able to be read in immediately. For example, if a programmer had just coded an ADD instruction at address 400, and the ADD instruction required 4 word-times to execute, the programmer would set the "Next Address" field of the instruction to 404, and would place the next instruction there.

In the United States, optimum coding was most commonly employed on the IBM 650 and the Bendix G-15. Both machines had optimizing assemblers (SOAP for the IBM, POGO for Bendix) that could automate this task.

PB 250

The PB 250 (later Raytheon 250) was a general-purpose computer introduced in 1960 by the Packard Bell Computer Corporation.Central Computer weighed 110 pounds (50 kg).

Richard V. Andree

Richard Vernon Andree (16 December 1919 – 8 May 1987) was an American mathematician and computer scientist.

Andree taught at the University of Oklahoma for 37 years, and served as a professor emeritus there until his death. He and his wife, Josephine, founded the Mu Alpha Theta mathematics honor society. Andree wrote a book on abstract algebra entitled Selections From Modern Abstract Algebra which was first published in 1958. He also wrote and published at his own expense numerous puzzle books and enjoyed cryptography. Andree and his students developed the ALPS programming language for the Bendix G-15 computer.

For several years in the late 1960s and thru the 1970s, Andree ran a summer school for high school teachers in Oklahoma to expose them to computers. Teachers would come from around the state and take short courses in programming in FORTRAN or BASIC. He also held evening and night computer study labs for local business owners wanting an exposure to computers and how they could use them in their business.

Andree was influential in the national collegiate mathematical organization Pi Mu Epsilon, having served as President, Secretary-Treasurer, and editor of their Journal. The Richard V. Andree Awards are given by the organization to undergraduates whose articles in the Pi Mu Epsilon Journal have been judged as containing the best content for the year.

Serial computer

A serial computer is a computer typified by bit-serial architecture — i.e., internally operating on one bit or digit for each clock cycle. Machines with serial main storage devices such as acoustic or magnetostrictive delay lines and rotating magnetic devices were usually serial computers.

Serial computers required much less hardware than their parallel computing counterpart, but were much slower.

ZEBRA (computer)

The ZEBRA (Zeer Eenvoudige Binaire Reken Automaat translated Very Simple Binary Automatic Calculator) was one of the first computers to be designed in the Netherlands, (the first one was the "ARRA") and one of the first Dutch computers to be commercially available. It was designed by Willem van der Poel of the Netherlands Post, Telegraph and Telephone, and first delivered in 1958. The production run consisted of fifty-five machines, manufactured and marketed by the British company Standard Telephones and Cables, Ltd.

The ZEBRA was a binary, two-address machine with a 33-bit word length. Storage was provided by a magnetic drum memory holding 8K words; accumulators were also implemented as recirculating drum tracks in a manner similar to that used in the Bendix G-15. Peripherals included paper tape reader and punch, and teleprinter.

In 1967, six Zebra computers were in use in UK universities and technical colleges.

Related articles

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.