Computer Space ram

Determining the amount of RAM in this is a little more difficult. It didn’t have ram chips, like modern machines. But instead used ttl counter chips. Inside a counter chip you have 4 flips flops wired together, to keep track of numbers 0-15. A flip flop is created by connecting together two AND gates, inverting the outputs, and connecting them back to the input. This makes a SR flip flop, or set reset flip flop. Which allows one wire to be set, making the output high or 5 volts, and the other wire would be reset, switching the output to low or 0 volts. The foundation of all memory today. This isn’t RAM, because it’s not random access memory. This is dedicated memory. When this was designed counter chips were petty common. Looking through the schematics you’ll see a number of them. The 74161, is a 4 bit counter, it will store numbers between 0 and 15. You can increment these and reset them to zero. If you connect two together, they can store numbers from 0 to 255. Which is 1 byte of memory. The 7490 is another counter it also stores 4 bits of data. Why use two different types? Probably the 74161 was a little cheaper. The 7490, was a little more capable. It could count in decimal 0-9, base 12 0-11, or hex 0-15. This chip is used so that the machine could count in decimal, this is important for display. Because most humans prefer to think in base 10. They didn’t expect anyone to get 10 points, so they didn’t implement proper display for scores over 9. Although you can get upto 15 points, it wouldn’t show properly. When you reached 16 points, you score rolled over to zero, and you started over agan. Things that the machine would need to keep track of included, the Player Ship, Computer Ship, number of deaths of each, time left to play, missles. For the player ship, we need speed x, speed y,current x, current y, and the angle of the ship. Then the missle needs x,y,and angle as well. That’s about 6 bytes. We also need that for the computer as well. Then we need one byte for the score, and 1 byte for the timer. That’s 14 bytes so far. Then we need the horizontal and vertical position that’s being sent to the tv, another 2 bytes. So this whole machine would need less than 20 bytes of memory, which would take 40 counters. Computer Space had the equivalent of 2 bytes of RAM.

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