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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.

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Updated April, 2016