The DDP-516 computer was originally designed by Computer Control Company Inc, who were bought out by Honeywell in 1966. This machine uses plug-in modules, each containing several IC’s to form a logical function. This greatly reduced the size of the computer.

If you haven’t heard of Honeywell computers it is prehaps because the minicomputer division almost disappeared as Honeywell was concentrating on mainframes. However there are two historical milestones in the history books. First of all, the DDP-116 was the worlds first commercially available 16-bit computer. The DDP-516 has prehaps even greater historical significance. Back in 1967 the Advanced Research Projects Agency (ARPA) started thinking about how to link several computer systems together across the country (US) in order to share information easier.

They had decided to use the DDP-516 computers as Interface Message Processors (IMP). Their task was to relay data over a network from one node to another, routing the data to the correct place, buffering data and checking for errors. A modern equivalent would be a network router.

The application for which the DDP 516 is best known is in the origins of the internet ARPA net. They were used as the main computer to create a “Interface Message Processors” or IMP. They named the network ARPANET. By 1971 there were 15 nodes, using DDP-516 computers as IMPs, connecting 23 mainframe/mini computers (hosts). It was able to run at 50kpbs.

The first DDP-516’s were rugged computer versions. This made them expensive, but very reliable. They had 24kbytes of core memory and each IMP could support 4 local hosts and connect to 6 other IMPs. As technology improved and prices came down, the 316 was used on some IMPs instead of the higher priced DDP-516.

Later on ARPA allowed universities to connect to ARPANET, allowing research to be easily shared between different groups. One noticable area of research was improvements to Wide Area Networks, such as ARPANET.

The other significant historical fact was the DDP-516 was used by the National Physics Labratory in England in 1967 to design and test the first packet switching Local Area Network. This network type was what ARPANET would connect together to form a Widea Area Network.

In 1988 ARPANET was taken out of service and was replaced by a new system, known as the World Wide Web, otherwise known as the Internet. The WWW is based on ARPANETs original idea, only with significantly modernised technology.

Also see Adrian Wises’ page on the Series-16 computers.

7 thoughts on “Honeywell DDP-516

  1. cara Reply

    Would be interesting to find out something about the Software used in DDP515 and also for the IMP controlls. I worked in GDR (DDR) on the DDP516 “fork” the KRS4200 with the Assembler and some bare-metal interpreter called DIWA. This was nothing near Basic. This was a otherwise constructed language on german nouns and verbs and for practic use also taken mostly as abreviations. Was on original DDP516 something like this? Are some digitalised manuals in your arcive? The PDP8..11 archaelogy has some good stuff of it, but it seems the DDP516 material outside of the kitchen-calc-poster has gone away in a state of very increased entropy 😉

  2. Jack Smith Reply

    I worked on a DDP-516 in 1970. It was strictly 16-bit assembler then. There was no operating system. It was a good way to learn computing fundamentals.

    • Georges E. Melki Reply

      I had exactly the same experience: back in 1970. The Lebanese government bought a Boeing 720 Digital Flight Simulator from Redifon- England, on which I worked as Simulator Engineer for 7 years. It was driven by a DDP-516, with a 16-bit Assembler. Back then, it was the ‘nec plus ultra” of digital computers. It was fun to follow the program, of which we had a printout, instruction by instruction, and also to input instructions via the console, especially the “key-in loader”
      Good old days…followed by very bad days starting in 1975!
      NB- The Simulator with all its auxiliaries(computer, teletype, paper punch, linkage, peripherals etc…) was dismantled by the Israelis when they occupied Beirut in 1982.

  3. max Reply

    A mostly opCode compatible system was implemented on TTL-hw in the 70’s DDR (GDR, eastern germany). Was called KRS4200 aka P4000; 4201 etc. … more than 1000 devices worked allaround the GDR-science and industry.

    A to this derivate binairy compatible Hw-Emulator as part of a PDP11-derivat (Robotron A6402) runs faster than origin.

    Details on

    Doe have information about such subjects?
    please be free type it in:


  4. K C Moore Reply

    Am I right in remembering that the DDP 516 and later the DDP 316 were used by ESTEC to record the testing of spacecraft in simulated launching stresses and space temperatures? If so, then there may have been two implementations of a compiler for a PL360-like programming language for these computers. I was in Mathematics Department at ESTEC from 197o to 1973, and, not knowing about the NPL language at the time, recommended to my colleague responsible for the programmers of these test programs that he obtain a PL316 for efficiency and quick transfer to later computers with the same instruction set.

  5. James Lynes Reply

    I worked on the most visible application of the DDP-516 starting in 1973. This would be Disney’s Digital Animation Control System(DACS). Our DDP-516s were able to support via a custom disk controller 8 128K word fixed head disk drives as well as 4 CDC 9-track reel-to-reel tape drives. The 516 supported a Disney feature film artist in the creation of the data that drove the Audio Animatronic attractions at Walt Disney World beginning in 1971. The animation data was played back by a Show Control Unit – a rack of TTL cards designed by AstroData Corp. The software was all assembly language. The original development started in 1969 I believe. The two original developers came to Disney from Singer Librascope where they designed submarine fire control systems. What you could do with 32KWs of memory in those days!

  6. Chris Stacy Reply

    This is a great article but is very confused when it gets to the part about the ARPANET being retired. The Internet came online in 1982, not 1988, but the main backbone network was still those H-316 IMPs, with slightly updated software, and the hosts all running TCP/IP. I don’t remember when we turned off the IMPs but 1988 sounds plausible; someone can look that up.

    And most certainly the WWW has nothing to do with the Internet. It’s just an application that you can run on the Internet — the web is NOT the Internet!

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