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How computers compute

Video transcript

[MUSIC PLAYING] Even though we think of computers as super-complicated, high-tech machines with very tiny parts, they can also be huge, wooden, and mechanical just like this computer here. And even though they look very different, they're both made of the same basic part, a switch. One switch doesn't seem very interesting. It's either off or on. But if we arrange switches in a specific pattern, we can do math or logic. For instance, this circuit turns on the light if both switches are turned on. But this circuit turns on the light if either or both switches are turned on. If we connect more switches, we can do more complex math and logic. So fundamentally, a computer is just a carefully constructed arrangement of switches. A light switch has a mechanical input and an electrical output. But because the input and output types are different, we can't connect the output of one to the input of another. In order to make more complicated circuits, we need a switch with the same input and output types so that we string a bunch of switches together. Our Digi-Comp has switches with a mechanical input and mechanical output. Just like the light switch, these switches have two states, either left and right, off and on, or 0 and 1. What's really cool here is that instead of programming this computer by writing code, we program it by physically setting the position of several different switches. I'll now set this computer to count the number of balls in the top tray by setting the count switch to on. The sum is given by this bank of switches here. We'll set the sum to 0 before we start counting. Now let's start counting by pressing this lever. [MUSIC PLAYING] The math problem the computer solved was 0, 0, 0, 0, 0, 0, 0 plus 1. As the ball goes through the system, it changes the first switch from a 0 to a 1 so that the sum now reads 0, 0, 0, 0, 0, 0, 1, or simply 1. Now let's count the second ball. [MUSIC PLAYING] So what happened this time? I'll reset the sum back to 1. The math problem that we solved was 0, 0, 0, 0, 0, 0, 1 plus 1. The Digi-Comp adds 1 to the first switch. But since it's already full, it carries the 1 to the second switch. The sum ends up being 0, 0, 0, 0, 0, 1, 0, which is 2 in binary. Let's count the third ball. [MUSIC PLAYING] After the third ball, we can see that the sum is now 0, 0, 0, 0, 0, 1, 1, which is 3 in binary. In addition to counting, the Digi-Comp can add, subtract, multiply, and divide. The number of switches determines how big the numbers can be. This Digi-Comp has 31 switches and can count up to 127. Well, modern computer chips have over a billion switches. They're made from wafers such as this one, where each square represents a chip. They're made from semiconductor switches called transistors, which have the advantage of being solid state, meaning they have no moving parts. This allows engineers like me to make them smaller, faster, and more energy efficient. We can make them over a billion times faster than the Digi-Comp. These semiconductor switches make modern electronics possible. [MUSIC PLAYING]