How to write a game for a computer that has no input and output devices

What can be done with a computer on electromagnetic relays which has no input devices, and from output devices only a dump of eight registers?

Play games, of course! The ancient people played on the MK-61/52 calculators, which are only slightly clearer.

Guess the number

I started with the game, where the computer with the help of the half division should find the integer from 0 to 100, which the player has thought up.
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The computer writes its guess on register A, and then stops.

The values ​​of all registers can be seen thanks to the LEDs built into the relay:



Now the player must change the program code in the ROM, replacing the constant that is loaded into the register D. If there is not 0, this means that the assumption is greater than the guess number. Otherwise - less. After that, you need to press the "continue" button. Checking the register D, the computer uses the previous assumption as the upper or lower limit in the next attempt.




The disadvantage of the first program is that it is inconvenient to use. This can be understood by looking at the photograph of the ROM - it is not very easy to switch such small toggle switches while playing the game (and you also have to make sure that the program doesn’t spoil the program accidentally).

So I came up with another input option. For debugging , a toggle switch is provided next to each register to reset its value. Its switch is much more convenient than changing the ROM.

Now the computer enters the unit in register D in advance, and the player either drops it (if the guess is less than the intended number), or leaves it as is (if the guess is more).

Subtraction game (Bache game)

Another classic game that is often implemented by novice programmers is the Bache game.
In it, two players from a handful containing initially N items take turns taking at least one and no more than M items. The loser is the one who has nothing to take.



In my version the game goes with a computer. Initially, a handful of 21 items (for example, 21 matches). Players take 1 to 3 matches in their turn, and the one who takes the last match wins.

The game has a winning strategy for the first player - always keep the number of matches, which is a multiple of four. Since 0 is also a multiple of four, the second player will not be able to bring the game to this position, which means he will lose.

The computer goes second, leaving a chance to people, but it does not make mistakes. And if the player does not follow the winning strategy, then the computer will do it.


In the first version, the same approach was used as for “guess the number” - in its turn it was necessary to encode the number of matches inside one of the instructions. It was even possible to count and take all the matches at once, but the computer would not notice anything.

But then I rewrote this program too. Now in three registers (B, C, D) the computer enters 1 each, and the player must reset 0, 1 or 2 of them. The remaining units are those matches that he takes. Cheat, too, can be, if you reset all three registers (as if you do not take anything).


Of course, the program turned out to be somewhat longer, but it is much more convenient to use it.


Next, I plan to add a ROM (now there are only 32 words out of a possible 64), and also to add an input device in the form of a matrix from toggle switches. Maybe then it will turn out to make at least tic-tac-toe.