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## Engineering and electronics

Current time:0:00Total duration:4:22

# 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]