Computer Space Replica Is Up And Running

You never forget your first time — watching someone pour several quid’s worth of 10p pieces into a Space Invader machine in 1978, upsetting for a youngster who wanted to have a turn. We’re still waiting, but [Alston] has found an interesting way to get around those arcade video game hoggers by building a replica of Computer Space, the first commercial arcade video game.

Released in 1971, the groundbreaking game was designed by gaming legends [Nolan Bushnell] and [Ted Dabney], and came in a striking curvy fiberglass case that was molded by a manufacturer of swimming pools. [Alston] hasn’t built the case yet, but he does have the electronics up and running.

The electronics of Computer Space are interesting, because there is no microprocessor in there. Instead, it is built from discrete components. [Nolan] had originally planned to use a mini computer called the Data General Nova 800. However, he realized that he could make it cheaper by building it out of discrete components. As [Nolan] described it in an oral history at the Smithsonian [PDF link], the idea came to him after a post-Thanksgiving dinner nap:

“Screw the minicomputer. Get rid of it. Do it all in hardware. Make the game out of this collection, just make it a simple state machine. And the minute that happened, it was like knife through butter. Not only did I get the cost down, but what was budgeted for $1,500 worth of minicomputer, the whole damn computer cost me less than $300 in glue parts. So, I knew that I had something.”

That decision makes it an interesting project to build a replica. Although you can emulate it on a modern computer easily (there is even a version that runs in CSS in the browser). [Alston] is going the hard route, building replica PCBs and using the same components where possible, helped by people who have documented it. So far, the boards are and running and displaying a grainy, pixelated image on a portable TV.

The next step is to take the replica electronics box he has built and make a cabinet to put it into. That’s a big project, and [Alston] is looking for someone with an original cabinet that he can examine and document.

8 thoughts on “Computer Space Replica Is Up And Running

  1. I remember dropping some quarters in such a machine.
    It may have left a negative impact on future gaming, losing money to learn how the games work.

  2. Space Invaders was also huge boards covered in TTL logic- a state machine, no CPU.
    Problem was it had a bug… you could stay alive hiding under a certain spot on the rightmost island. Word got around and the game had to be shut down.
    Tech comes to fix it, and “firmware” fix was really adding jumpers, IC’s glued on top of others etc.
    pages of instructions. They were so pissed at how much rework had to be done. This was in 1980.
    A warning that any bugs here needs soldering to fix!

    1. Space Invaders did have a lot of special helper hardware like external shift hardware, but it was based on the Intel 8080. The player, bullets, and saucers are interrupt driven thus always the same speed, while the invaders are driven by the main program loop which loops faster as there are fewer invaders to manipulate.

      1. I don’t remember seeing anything DIP-40 on the vertical board at the back. Monochrome version, blue cabinet circa 1980. Acres of small DIP IC’s.
        Interesting the bug fix required H/W mods – it was as if there was a dead column where aliens fired. The guy would shoot a whole in the far right shield and pick off the invaders there coming down fast at the end, he never got fired at. It was a Taito or Bally design?

        1. Actually I cannot remember either one as the maker. But I do recall what was used as the sound maker chip for it. It was the first mainstream use of the TI SN76477 sound maker.

    2. There was an 8080 processor in “Space Invaders”, both Taito (2 or 3 boards stacked) and Midway (“L” shaped boards). The Midway version was strictly B/W (AFAIK), while the some Taito’s had a special section on the boards that would use PROMs to run a little bit of code that would decode the position the screen was drawing and would apply colors accordingly.

      The game had several EPROMs/PROMs in there that held the program itself. IIRC, it was either 4 or 8 chips depending the size of the EPROM/PROM used. With higher capacity EPROMs more readily available most people have modified their boards to use a single 2764 EPROM to eliminate any issues with failing sockets (fewer connections = fewer problems). Since the same hardware was used in several games, you could actually use even bigger EPROMs to hold completely different games and could change them with switches. Works really well on B/W boards since the color PROMs are based off of screen position and not the program running… so it will happily apply the colors to places that don’t make any sense on other games. When you change different families of EPROMs, you also have to change the “strapping” which are jumpers that move voltages and address lines around to match the chips… even WITH the available information, re-strapping these boards is a PITA.

      Both used dedicated circuits for each sound, usually based on LM3900s, 556s, and 76477s for the saucer sound. You could fine tune each sound’s volume with a potentiometer, or customize them if you wanted… but no-one really did on purpose… but they would sometimes use different value capacitors if they broke off and you would end up with machines that sounded a little different. My Midway “Space Invaders” sounds really weird because whoever worked on it originally, BITD, just threw whatever caps they had on hand in there… I left it like that because it’s “history”, but mainly because I’m “lazy.” The sound’s volumes are important to keep in mind if you live with other people and get the urge to play early in the morning or late at night because the “thud” sound whem the invaders move is VERY “bassy” and should be turned down, a lot, if you don’t want to wake EVERYONE up. has some REALLY great information on these boards as well as updated schematics since original scans are, well… a nightmare to read TBH.

      I saw it in a comment further down… but the really neat thing about this game is the first (AFAIK) bug that became a feature. There just wasn’t enough processing power in the 8080 to move all the invaders efficiently. So the fewer invaders on the screen, the faster it runs. So it speeding up as you shot more invaders wasn’t fully intended, but it just became part of the game.

      There is also an Easter egg in the original code as well… this is copied from as I can never remember it off the top of my head as I did it a couple of times to test and then just never bothered with it again:


      There is a hidden message in the Space Invaders code. You can get the message “TAITO COP”, with no “R” as in “CORP”, to appear at the top of the screen during the demo play. Wait for the demo play to start and hold down “2 Start”, “1 Fire”, “1 Left”, and “1 Right”. The order you press them and the timing does not matter as long as you get all the buttons down at the same time eventually.

      That’s the first sequence. Then you have to hold down the second sequence: “1 Start”, “1 Fire”, “1 Left”. Again the timing does not matter. An easy way is to hold down the first sequence and just switch start buttons and let up on “1 Right”. You will see the message at the top of the screen in the “Flying Saucer” area (in red). The message will be erased when the demo finishes and you will have to reenter it every demo.


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