Part 7 of a series: Bendix G-15 Restoration

There is nothing I can add to the volumes that have already been written about Alan Turing, so I’ll use this post to collect interesting links, especially with references to the Bendix G-15.

Wikipedia: Alan Turing

Alan Mathison Turing 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 formalization of the concepts of algorithm and computation with the Turing machine, which can be considered a model of a general-purpose computer. He is widely considered to be the father of theoretical computer science and artificial intelligence.

I recently read “Alan Turing’s Electronic Brain” and it is a very good read for anyone interested in the Bendix G-15, as it details the evolution of the instruction set, drum memory, etc.

Amazon: Alan Turing’s Electronic Brain

The mathematical genius Alan Turing, now well known for his crucial wartime role in breaking the ENIGMA code, was the first to conceive of the fundamental principle of the modern computer-the idea of controlling a computing machine’s operations by means of a program of coded instructions, stored in the machine’s ‘memory’. In 1945 Turing drew up his revolutionary design for an electronic computing machine-his Automatic Computing Engine (‘ACE’). A pilot model of the ACE ran its first program in 1950 and the production version, the ‘DEUCE’, went on to become a cornerstone of the fledgling British computer industry. The first ‘personal’ computer was based on Turing’s ACE.

I recently watched “The Imitation Game” and highly recommend it.

Amazon: The Imitation Game

During the winter of 1952, British authorities entered the home of mathematician, cryptanalyst and war hero Alan Turing (Benedict Cumberbatch) to investigate a reported burglary. They instead ended up arresting Turing himself on charges of ‘gross indecency’, an accusation that would lead to his devastating conviction for the criminal offense of homosexuality – little did officials know, they were actually incriminating the pioneer of modern-day computing. Famously leading a motley group of scholars, linguists, chess champions and intelligence officers, he was credited with cracking the so-called unbreakable codes of Germany’s World War II Enigma machine. An intense and haunting portrayal of a brilliant, complicated man, The Imitation Game a genius who under nail-biting pressure helped to shorten the war and, in turn, save thousands of lives.

Next: TBD

Part 6 of a series: Bendix G-15 Restoration

The chief designer of the Bendix G-15 was computer pioneer Harry Huskey who based it on the Automatic Computing Engine (ACE) designed by Alan Turing at the National Physical Laboratories in Britain. Huskey had worked with Turing there for a year. Much of this post is taken from the Harry Huskey website. There is also some good information at Wikipedia: Harry Huskey and CHM: Harry Huskey. His obituary is here: Computer pioneer Harry Huskey dies at age 101.

Dr. Harry Huskey was born in the Smoky Mountains region of North Carolina and grew up in Idaho. He gained his master’s degree and then his PhD in 1943 from the Ohio State University on Contributions to the Problem of Geocze. Harry Huskey taught mathematics at the University of Pennsylvania and then worked part-time on the early ENIAC computer in 1945.

Harry Huskey designed and managed the construction of the Standards Western Automatic Computer (SWAC) at the National Bureau of Standards in Los Angeles (1949 to 1953). He also designed the G15 computer for Bendix Aviation Corporation, which could perhaps be considered as the first “personal” computer in the world. He had one at his home that is now in the Smithsonian Institution in Washington, D.C.

I’ll add more information about Harry Huskey as I find it.

Next: Bendix G-15: Alan Turing

Part 5 of a series: Bendix G-15 Restoration

One of the first things you discover when you start exploring the Bendix G-15 is that numbers are represented in base 16, but the hexadecimal (Greek root) A-F “digits” are not used for values 10-15. Instead, they use sexadecimal (Latin root) “digits”, where the values 10-15 are represented by the letters U-Z. Here’s more than you ever wanted to know about sexadecimal.

The Bendix Programmer’s Reference manual offers this (hilarious) definition:

“Hexadecimal” became a standard with IBM 360 Fortran

The now-current notation using the letters A to F establishes itself as the de facto standard beginning in 1966, in the wake of the publication of the Fortran IV manual for IBM System/360, which (unlike earlier variants of Fortran) recognizes a standard for entering hexadecimal constants. As noted above, alternative notations were used by NEC (1960) and The Pacific Data Systems 1020 (1964). The standard adopted by IBM seems to have become widely adopted by 1968, when Bruce Alan Martin in his letter to the editor of the CACM complains that with the ridiculous choice of letters A, B, C, D, E, F as hexadecimal number symbols adding to already troublesome problems of distinguishing octal (or hex) numbers from decimal numbers (or variable names), the time is overripe for reconsideration of our number symbols. This should have been done before poor choices gelled into a de facto standard!”

Bendix tried to make it easy

Next: Bendix G-15: Harry Huskey

Part 4 of a series: Bendix G-15 Restoration

I’m starting with what I’m calling the typewriter console, also known as the “Master Writer”, since it’s easily transported, fairly light and relatively robust compared to the fragile vacuum-tube CPU and magnetic tape mechanisms. I live in the mountains at the end of a long, bumpy dirt road and the thought of all those tubes and mechanisms bouncing around led me to find some spare office space down on the flatlands for most of the restoration, but I can work on the typewriter console at home.

The typewriter console is an interesting part of the system in that it’s based on an early IBM electric typewriter. Electric typewriters were often modified for use as input / output devices for early mainframes and minicomputers. The most commonly modified typewriters were made by IBM. In the 1950s, modified standard versions of the IBM Electric A, B, and C models were used as console typewriters or terminals on many early computers (e.g., GE 225, JOHNNIAC, IBM 650, IBM 1620, PDP-1). The IBM Selectric typewriter, introduced in 1961, was easier to interface to a computer and was favored in new designs, such as the IBM 1130 computer and the IBM 1050 terminal.

IBM eventually sold a modified version of the type called the “Input-Output Writer”. It was resold under a number of computer manufacturer names:

Here’s the console at the pickup, complete with dust. Now the fun begins!

Covers off!

It looks like I’m missing one of the toggle-switch caps on the typewriter base. I’ll need to find a matching replacement or fabricate one.

Next: Bendix G-15: Hexadecimal, Sexadecimal, Shmexadecimal

Part 3 of a series: Bendix G-15 Restoration

I finally got a good look at the Bendix today. It’s been in my friend’s garage for many years and has a fair bit of dust on it but it’s in great condition overall. I live in the mountains at the end of a very bumpy dirt road, so we’re going to transport the large, fragile components (CPU, 2 tape drives) to some spare office space I’ve located down on the flatlands to avoid any damage. I hate to think of 350 irreplaceable vacuum tubes rattling around in the back of a truck. I’ll bring the console, which is relatively small and light, up to my house and work on it here.

Some of the equipment has been used as a home by unwanted creatures. A contact at one of the large computer museums recommended that the contaminated equipment be disinfected by a professional pest control service. That’s what we’ll do!

Next: Bendix G-15: Typewriter Console

Part 2 of a series: Bendix G-15 Restoration

I’ll have lots more to say about the history of this fabulous machine later, but here’s a brief outline for now:

Next: Bendix G-15: Garage Archaeology

Part 1 of a series: Bendix G-15 Restoration 

I have a long-time friend who recently mentioned to me that he has an old computer in his garage that he’d like to find a good home for, preferably a museum.

“What type of computer is it?”, I asked.
“A Bendix G-15”, he answers.
“Oh cool”, I answered, having no clue what he was talking about.

I had to look it up and what I found is absolutely amazing.

The Bendix G-15 is a very early (1956) vacuum tube computer, based on Alan Turing’s Pilot ACE design, used primarily for military, scientific, and engineering. It was hailed as the first “personal computer” (meaning it only need one person to operate it) and was one of the very last vacuum tube computers produced. The base system, without peripherals, cost $49,500. A working model cost around $60,000 (over $500,000 by today’s standards).

It’s an odd beast, unlike any other computer I know of. It has a 29-bit word length, a whopping 2,176 words of magnetic drum memory, and an almost indecipherable instruction set. All operations are performed serially, 1-bit-at-a-time. It was gradually discontinued when Control Data Corporation took over the Bendix computer division in 1963.

There were only about 400 produced and they are quite rare now (this model is #350). One is in the Smithsonian, several are in museums around the world, and one is in my friend’s garage. There are several functioning G15s that I know of, one of which is a restoration commissioned some years ago by Paul Allen at the Living Computer Museum in Seattle.

The Bendix Corporation sold its computer division to Data General in 1963, so some of the last few G-15s produced (including this one) were badged as Control Data, but nothing is different underneath the hood.

The G-15 was well-known by many of the pioneers in our industry, including Donald Knuth, Ken Thompson, Paul Allen, Alan Perlis, Thomas Kurtz, David Evans, Ivan Sutherland, Elliot Organick, Mitch Kapor, David Ahl, Niklaus Wirth, John Backus, Vint Cerf, Seymour Cray, Max Palevsky, and Jeff Duntemann. For many of them, it was the first computer they used.

My friend’s G15 is in nearly mint condition, appearance-wise, but hasn’t been powered-up since 1979. Apparently, most of the 450 vacuum tubes have died an early death and most of the 3,000 germanium diodes have degraded to a direct short. Restoring it to full functionality would be extremely expensive, impractical, and I’m not even sure the fire marshal would allow it indoors. Some early users even relied on it to heat their offices. It would, however, make a magnificent museum display. It’s not as large as it looks in the photos. There are 3 units measuring 3′ x 3′ x 5′ and a teletype-style terminal. It is heavy, totaling over 1,500 pounds, and requires great care when transporting it.

To make a long story short, I have found a museum that wants the Bendix G-15 and I’ll be starting the long restoration (mostly clean-up) process soon! The goal is to clean it up, evaluate its condition, transport it to the museum, and put together a display.

Here’s a list of museums, no doubt incomplete, that have G-15s:

Vintage Computer Federation Museum (Wall Township, NJ, USA)
System Source Computer Museum (Hunt Valley, MD, USA)
Computer History Museum (Mountain View, CA, USA)
Living Computer Museum (Seattle, WA, USA)
Smithsonian National Museum of American History (Washington, DC, USA)
Ridai Museum of Modern Science (Tokyo, Japan)
Australian Computer Museum (Western Australia)

I have often forgotten to include before and after photos of my restorations, so I’ll make an extra effort to do so for this one, especially since it’s largely a cleanup operation.

Bonus! Here’s a fun video in which the Bendix G-15 saves the day!

Science Fiction Theatre: Dr. Robot (1956, Season 2, Episode 29)

The G15 appears in these time frames:

02:05 – 02:11
11:23 – 12:10
20:52 – 21:40

Another bonus: The Bendix G-15 plays a Christmas carol!

I’ve Got a Secret – Game Show

This is complex project, even if it is just cleaning and evaluation, so I’ve reached out to a few vintage computer groups:

VCF Minis and Mainframes Forum

Facebook Bendix G-15 Forum

Classic Computer Forum

Next: Bendix G-15: A Brief History