WEBVTT

00:00:06.681 --> 00:00:09.871
Modern computers 
are revolutionizing our lives,

00:00:09.871 --> 00:00:13.726
performing tasks unimaginable
only decades ago.

00:00:13.726 --> 00:00:17.209
This was made possible by a long series
of innovations,

00:00:17.209 --> 00:00:22.680
but there's one foundational invention
that almost everything else relies upon:

00:00:22.680 --> 00:00:24.198
the transistor.

00:00:24.198 --> 00:00:25.292
So what is that,

00:00:25.292 --> 00:00:30.403
and how does such a device enable
all the amazing things computers can do?

00:00:30.403 --> 00:00:34.239
Well, at their core, all computers
are just what the name implies,

00:00:34.239 --> 00:00:37.362
machines that perform 
mathematical operations.

00:00:37.362 --> 00:00:40.617
The earliest computers were manual
counting devices,

00:00:40.617 --> 00:00:41.929
like the abacus,

00:00:41.929 --> 00:00:44.341
while later ones used mechanical parts.

00:00:44.341 --> 00:00:48.752
What made them computers was having
a way to represent numbers

00:00:48.752 --> 00:00:51.171
and a system for manipulating them.

00:00:51.171 --> 00:00:53.423
Electronic computers work the same way,

00:00:53.423 --> 00:00:55.060
but instead of physical arrangements,

00:00:55.060 --> 00:00:58.870
the numbers are represented
by electric voltages.

00:00:58.870 --> 00:01:02.625
Most such computers use a type of math
called Boolean logic

00:01:02.625 --> 00:01:04.949
that has only two possible values,

00:01:04.949 --> 00:01:07.584
the logical conditions true and false,

00:01:07.584 --> 00:01:11.319
denoted by binary digits one and zero.

00:01:11.319 --> 00:01:14.246
They are represented by high
and low voltages.

00:01:14.246 --> 00:01:17.899
Equations are implemented
via logic gate circuits

00:01:17.899 --> 00:01:21.014
that produce an output of one or zero

00:01:21.014 --> 00:01:25.123
based on whether the inputs satisfy
a certain logical statement.

00:01:25.123 --> 00:01:28.834
These circuits perform three fundamental
logical operations,

00:01:28.834 --> 00:01:32.114
conjunction, disjunction, and negation.

00:01:32.114 --> 00:01:36.751
The way conjunction works is an "and gate"
provides a high-voltage output

00:01:36.751 --> 00:01:40.517
only if it receives 
two high-voltage inputs,

00:01:40.517 --> 00:01:43.158
and the other gates work 
by similar principles.

00:01:43.158 --> 00:01:46.594
Circuits can be combined to perform
complex operations,

00:01:46.594 --> 00:01:48.755
like addition and subtraction.

00:01:48.755 --> 00:01:51.393
And computer programs 
consist of instructions

00:01:51.393 --> 00:01:54.838
for electronically performing 
these operations.

00:01:54.838 --> 00:01:58.024
This kind of system needs a reliable
and accurate method

00:01:58.024 --> 00:02:00.243
for controlling electric current.

00:02:00.243 --> 00:02:02.785
Early electronic computers,
like the ENIAC,

00:02:02.785 --> 00:02:05.556
used a device called the vacuum tube.

00:02:05.556 --> 00:02:07.712
Its early form, the diode,

00:02:07.712 --> 00:02:12.316
consisted of two electrodes 
in an evacuated glass container.

00:02:12.316 --> 00:02:17.115
Applying a voltage to the cathode
makes it heat up and release electrons.

00:02:17.115 --> 00:02:20.492
If the anode is at a slightly
higher positive potential,

00:02:20.492 --> 00:02:22.839
the electrons are attracted to it,

00:02:22.839 --> 00:02:24.384
completing the circuit.

00:02:24.384 --> 00:02:27.346
This unidirectional 
current flow could be controlled

00:02:27.346 --> 00:02:29.766
by varying the voltage to the cathode,

00:02:29.766 --> 00:02:33.209
which makes it release more 
or less electrons.

00:02:33.209 --> 00:02:34.910
The next stage was the triode,

00:02:34.910 --> 00:02:37.875
which uses a third electrode
called the grid.

00:02:37.875 --> 00:02:41.484
This is a wire screen 
between the cathode and anode

00:02:41.484 --> 00:02:43.767
through which electrons could pass.

00:02:43.767 --> 00:02:46.243
Varying its voltage makes it either repel

00:02:46.243 --> 00:02:49.749
or attract the electrons 
emitted by the cathode,

00:02:49.749 --> 00:02:52.356
thus, enabling fast current-switching.

00:02:52.356 --> 00:02:57.577
The ability to amplify signals 
also made the triode crucial for radio

00:02:57.577 --> 00:03:00.085
and long distance communication.

00:03:00.085 --> 00:03:04.593
But despite these advancements,
vacuum tubes were unreliable and bulky.

00:03:04.593 --> 00:03:09.156
With 18,000 triodes, ENIAC was nearly
the size of a tennis court

00:03:09.156 --> 00:03:11.219
and weighed 30 tons.

00:03:11.219 --> 00:03:13.088
Tubes failed every other day,

00:03:13.088 --> 00:03:19.494
and in one hour, it consumed the amount
of electricity used by 15 homes in a day.

00:03:19.494 --> 00:03:21.460
The solution was the transistor.

00:03:21.460 --> 00:03:24.455
Instead of electrodes, 
it uses a semiconductor,

00:03:24.455 --> 00:03:26.992
like silicon treated 
with different elements

00:03:26.992 --> 00:03:29.926
to create an electron-emitting N-type,

00:03:29.926 --> 00:03:32.655
and an electron absorbing P-type.

00:03:32.655 --> 00:03:35.418
These are arranged in three 
alternating layers

00:03:35.418 --> 00:03:37.202
with a terminal at each.

00:03:37.202 --> 00:03:39.933
The emitter, the base, and the collector.

00:03:39.933 --> 00:03:42.155
In this typical NPN transistor,

00:03:42.155 --> 00:03:45.373
due to certain phenomena 
at the P-N interface,

00:03:45.373 --> 00:03:50.398
a special region called a P-N junction
forms between the emitter and base.

00:03:50.398 --> 00:03:52.491
It only conducts electricity

00:03:52.491 --> 00:03:56.604
when a voltage exceeding 
a certain threshold is applied.

00:03:56.604 --> 00:03:58.990
Otherwise, it remains switched off.

00:03:58.990 --> 00:04:02.339
In this way, small variations 
in the input voltage

00:04:02.339 --> 00:04:07.130
can be used to quickly switch between
high and low-output currents.

00:04:07.130 --> 00:04:12.186
The advantage of the transistor lies
in its efficiency and compactness.

00:04:12.186 --> 00:04:16.564
Because they don't require heating,
they're more durable and use less power.

00:04:16.564 --> 00:04:22.332
ENIAC's functionality can now be surpassed
by a single fingernail-sized microchip

00:04:22.332 --> 00:04:24.612
containing billions of transistors.

00:04:24.612 --> 00:04:27.057
At trillions of calculations per second,

00:04:27.057 --> 00:04:30.541
today's computers may seem like
they're performing miracles,

00:04:30.541 --> 00:04:31.795
but underneath it all,

00:04:31.795 --> 00:04:36.555
each individual operation is still
as simple as the flick of a switch.