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Bendix G-15

Manufacturer Bendix
Identification,ID G-15
Date of first manufacture1956
Number produced about 300
Estimated price or cost"$50,000 in late 1950 dollars"
location in museum -
donor -

Contents of this page:

Photo Photo
Bendix G-15
Opened for detail 74 K Bytes

Bendix G-15 - by Ron Mak

  • Two address, drum main memory,
  • Word length - 29 bits
  • Optional magnetic tape storage
  • Double-length arithmetic registers for machine supported double precision

Special features
  • Block I/O permitted movement of up to 108 words with a single command
  • Simultaneous I/O and computation
  • The following interesting peripherals were available
    • An accessory "DIGITAL DIFFERENTIAL ANALYZER DA-1" greatly eased and speeded certain engineering work.
    • Graphical Plotter PA-3
    • Punched Card Coupler CA-2
    • Punched Paper Tape Reader PR-1 (250 character/sec), PR-2 (430 characters/sec, can read 5, 6, 7, or 8 bit tape, searchable)
    • Special Input-Putput Registers
  • Gordon S. Becker - - says " I was in charge of a scientific computing division for the U.S. Army Map Service and the cost for G-15D computer (The D postscript denotes an alphabetic capability) was in the neighborhood of $50,000.00 in late 1950 dollars. I also have retained copies of the coding for a number of double precision computer programs. ..."

Historical Notes
  • Same year, similar use of circulating registers on drum as LGP-30
  • Followed by the transistorized Bendix G-20

This Specimen

Interesting Web Sites

Other information -
BRL-61 Link

from Rob Kolstad, Dec 2008
I have identified perhaps half a dozen extant G-15s, including one at the [Computer History Museum]. I have built a paper tape reader so I hope to get all the software (!) up and running on the simulator that I'm reworking from the australians (who originally wrote the simulator in SIMULA-60).

Its architecture is so simple that it lends itself to a fabulous evolution-of-computer-architecture exhibit -- especially since it's arguably the first Personal Computer (!).

          ((__))       Rob Kolstad                      USACO Head Coach
           (00)   15235 Roller Coaster Road  
     -nn--(o__o)--nn-  +1 719 481 6542        Colorado Springs, CO 80921
           ----        Cell: +1 719 321 7333

from Douglas Drummond, April 2016
I used a G-15 from 1963-1965 at Rose Polytechnic Institute in Terre Haute Indiana. The school is now known as Rose-Hulman Institute after Tony Hulman (Owner of the Indianapolis 500 Race Track) died and left them a ton of money. I am a retired hardware/software engineer and currently tutor computer science and teach it at a community college in the Chicago suburbs.

For my own research, I am currently writing a G-15 simulator in Java on a PC, with a fairly decent GUI representing the front panel display. My typewriter simulation uses Alt-codes to simulate Enable codes, with a few additions. When I was in college 50 years ago, I programmed the G-15 in machine language. At the time, we G-15 machine language programmers said we will probably never see an instruction set any weirder that the G-15. Although the CDC-6500 and the Burroughs D-Machine came close, I still believe that.

On your web site, you asked for feedback from anyone who knew anything about the G-15, so I am emailing. One result of my research is that I am pretty sure of the alphanumeric codes, which I extracted from the schematics of the Alpha hardware.

Previously I wrote a simulator for the LGP-21, the transistorized version of the LGP-30, with MUCH better I/O. I re-used much of that code for the G-15 simulator, and plan an RPC-4000 sim. Since that instruction set is so simple I am working on tutorials using that simulator as a "generic" binary computer for teaching embedded programming and machine/assembly language principles. I did have "hands on" an LGP-21 in graduate school in 1970, which was really an "antique restoration project" even 45 years ago. I also used an RPC-4000 at Purdue in the late 1960s, a direct descendant of the LGP-21/30.

2022 - Emulator from Paul Kimpel June 26, 2022

Just FYI, I have recently written an emulator for the G-15. It is open-source and publicly available. I thought you might want to add this information to the G-15 page on your web site.

My emulator is written using JavaScript/HTML/CSS and runs in a standard web browser. It attempts to run at the speed of a real G-15. At present it supports only paper tape and typewriter I/O, but I am interested in implementing additional devices once I find software available that can use them. The emulator successfully runs diagnostics tapes I acquired from David Green's and Paul Pierce's web sites and appears to run properly the ubiquitous PPR (Program Preparation Route) utility supplied by David. It even runs a somewhat notorious four-word program that cleared all of memory, the registers, and the overflow and multiply/divide sign flip-flops.

If you need any additional information, please let me know.

2022 - Documentation List from Rob Kolstad October 3, 2022
Dear Fellow G-15 Enthusiast,

I'm Rob Kolstad, and I am sending you this little informational blurb because I think you are interested in Bendix G-15 projects (sometimes because I have seen someone messaged you about such things in the last two decades). Feel free to send me an 'unsub' note to never hear again about such things.

This note announces the beta test of the first set of the documentation collection:, local copy

The collection includes 161 source documents (some duplicates) comprising some 10,566 pages (including blanks). I have broken some of the source documents into their constituent sub-documents (e.g., the Technical Application Memos) for easy access, yielding 1,414 documents in total.

The collection is by no means complete (coming soon: good large-format schematics and perhaps a search bar), but it's a good start. I'll try to scan the rest before the year is out.

The fine folks at the System Source Computer Museum in Baltimore have gained, at least for now, several Bendix G-15's (and peripherals) along with more than two dozen boxes of Bendix documentation mingled with documentation of a large highway engineering firm's projects. The collection also has hundreds of paper tapes in fabulous condition.

I scanned a fraction of these documents back in June and combined them with my personal collection (thanks to Bob Sander-Cederlof in Texas) and the documents from and the Computer History Museum (among others).

This documentation section forms one of the main parts of the soon-to-be-released (2022) website for all things G-15, including software, hardware/restorations, emulators, news, photos, and notes.

Please feel free to check out the documents. I'll let you know in a few months when the general web-site is available. Comments, questions, and suggestions are always welcome.


            /\      Rob Kolstad                                 Delos
     /\    /  \   15235 Roller Coaster Road  
    /  \/\/    \                           Colorado Springs, CO 80921
   /    \ \     \                              Phone: +1 719 481 6542

2022 - G-15 like Turing's ACE computer
from Jim Holtman - Nov 25, 2022
This was the first computer I programmed working as a co-op student at White Sands Missile range 1962-1967.
It was a while before I realized it was based on the ACE computer developed by Turing.
I was wondering if anyone remembers the 4 words instructions you could type in on the console that would clear memory; this program had to fit is a short line (4 words) and was an interesting piece of code.

If you have comments or suggestions, Send e-mail to Ed Thelen

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Updated June, 2022