©Mark Ollig
In the summer of 1981, yours truly was using a Sinclair ZX81 computer to add information to a program I had coded.
Typing on the small keyboard, I watched the words and numbers appearing on the monitor of the portable black-and-white television I borrowed from the living room and connected to the ZX81’s video output.
The ZX81 stored my program on a cassette tape; yes, a cassette tape recorder was connected to the computer, too.
As I recall, the program stored on the cassette tape kept track of ongoing maintenance and other information regarding my 1976 Plymouth Duster.
For the younger folks; Plymouth was a brand of cars manufactured by Chrysler, and my highly-treasured Plymouth Duster was equipped with a four-speed manual/Hurst shift.
I enjoyed driving my Duster, too. Shifting gears was effortless and a lot of fun; it was “like a hot knife going through butter,” as they used to say.
However, I digress.
The 1956 glossy brochure for the Bendix G-15 electronic computer advertised it as “a complete computational facility” and a “general purpose digital computer.”
The G-15, a minicomputer, could be operated by one person, instead of the several needed for the larger and more complex computing systems of the time.
Might the G-15 be considered a personal computer, since it only needs one person to operate it?
The G-15 digital computer was built by the Bendix Aviation Corporation, headquartered in Los Angeles, CA, using the drawings and designs they purchased from American computer designer, Harry Douglas Huskey.
Huskey worked at the National Physical Laboratories in Britain for a year with the famous mathematician, computer scientist, and cryptanalyst, Alan Turing.
It should be noted, the Bendix G-15 was mostly based on Turing’s design of an Automatic Computing Engine (ACE) electronic stored-program computer he described in 1936, as a “universal computing machine.”
The G-15 was used mostly for scientific and engineering purposes; however, in 1961, Bendix produced a G-20 mainframe computer for business use.
The metal cabinet of the Bendix G-15 was the size of a refrigerator, painted with a very deep shade of gray mixed with blue.
Its physical dimension was approximately 5 feet by 3 feet.
The Bendix G-15 weight was listed at 850 pounds in their 1956 brochure – other sources say 950 pounds.
OK, so the G-15 was not a portable computer one would bring into the coffee house and place on the table next to your cup of latte.
Remember folks, I said it was possibly the first personal – not carry-with-you – computer.
The G-15 computer console keyboard, called the “Master Writer,” was an electric IBM modified typewriter connected onto a base housing and cabled to the computer using a 61A37 connector.
The G-15 recognized typed data input at a maximum speed of eight characters per second.
Other ways to input programs into the Bendix G-15 included using perforated high-speed paper tape, standard IBM punched cards, and pre-programmed commands stored on external magnetic tape units.
A programming language called the Intercom 1000 System was primarily used with the G-15 because of its easy-to-use interactivity.
FORTRAN, ALGO, and ALTRAN programming languages were also used with the G-15.
Up to four model MTA-2 magnetic tape units (each about the size of a small refrigerator) could be connected into a Bendix G-15 computer.
One MTA-2 magnetic tape drive unit stored 300,000 words of information using one-half-inch magnetic tape.
A paper digital graph plotter using a retractable pen was used to view output data at up to 12-inches-by-18-inches.
The G-15’s central processing unit (CPU) used vacuum tube technology with a processor clocking speed of 105 KHz (kilohertz).
The G-15 contained approximately 350 vacuum tubes, along with relays and electronic components, including resistors, capacitors, rectifiers, and inductors wired onto small, printed circuit board plug-in modules.
Specially configured diode component board-assembly packages for computing logic functionality were soldered on small printed circuit boards and physically mated with modules inside the G-15.
The vacuum tubes and electronic components were cooled via internal forced-air fans.
The G-15 computer was powered by standard 110-120 volt AC 60 cycles, single-phase input.
The Bendix G-15 computer’s magnetic drum memory stored more than 1,000 pretested programs a user/operator could choose from, using a single command.
The G-15 allowed for decimal input and outputs; however, internal computer processing used binary coding.
More than 400 G-15 computers were manufactured.
In 1956, the basic Bendix G-15A computer could be purchased for around $50,000, which, adjusted for inflation, equals a little more than $464,000 today.
Some of the data processing applications a Bendix G-15 computer was used for include:
• real-time data processing for the aircraft industry;
• processing missile trajectories and performance;
• mathematical analysis and academic research;
• computing teaching tool for universities; and
• engineering tool for design and construction.
A Bendix G-15 was installed for the US Navy in 1961.
In 1963, Bendix Corp. sold its computer to a Minnesota company based in Bloomington called Control Data Corporation, for “nearly $10 million in Control Data stock, cash, and other considerations,” according to a March 4, 1963, Minneapolis Morning Tribune article.
I encourage you to check out the 1956 16-page advertising brochure (with photos) of the “Bendix G-15 All Purpose Computer” at https://bit.ly/2PkaL1M.
The original 138-page G-15 model D parts manual includes photos, diagrams, and detailed explanations about the computer’s operation. I created this shortened link to it: https://bit.ly/2OKuDvs.
All in all, the G-15 was a well-thought-out, compact computer designed to require only one person to operate it.
Harry Douglas Huskey, who passed away at age 101 in 2017, had a working G-15 computer in his home.
He made the G-15 his personal computer.
