All language subtitles for 3_Programs the CPU and Memory

Before we get our hands dirty with
learning how to build a computer,

let's talk theory first.

In an earlier lesson,
we talked about binary and

how computers perform calculations.

Remember that our computer can only
communicate in binary using 1's and 0's.

Our computers speak in machine language
but we of course speak in human

languages like English, Spanish,
Mandarin, Hindi, you get the idea.

If we want to communicate with our
machines we have to have some sort of

translation dictionary, just like if I
wanted to say something in spanish I'd

look it up in an English
to Spanish dictionary.

Well our computers have
a built in translation book.

In this lesson we'll dive deeper into how
our computer translates the information we

give it into instructions
that it understands.

RIght now you're probably using a web
browser, music player, text editor or

something else on your computer.

We interact with these
applications on a daily basis,

they're referred to as programs.

Programs are basically instructions
that tell the computer what to do.

We typically store programs on
durable media like hard drives,

you can think of programs like cooking
recipes, we keep these recipes all stored

together in a cookbook,
just like apps stored in a hard drive.

Now we want to make a ton of food, so
we hire a chef to follow our recipes and

whip up something good.

The faster our chef works,
the more food she'll prepare,

the chef is our CPU she processes the
recipes, we send her and makes the food,

our chef works super fast so fast that
she can cook faster than she can read.

So we take copy of the recipes and
put them into RAM.

Remember that RAM is our computers short
term memory, it stores information in

a location our CPU can access it faster
than they could with our hard drive.

Now we can give our chef one or

two recipes at a time instead of
reciting the entire cookbook to her.

Okay, now let's say I want to make
a peanut butter and jelly sandwich.

I see a pretty good recipe and
send it to our chef to make,

remember that our chef needs
these instructions quickly so

I don't send her the entire recipe,
I sent her one line at a time.

One, get two slices of bread, two,
put peanut butter on one slice,

three, put jelly on another slice,
four, combine the two slices of bread.

Now let me throw one more thing at you.

Our chef can only communicate
with us in 1's and 0's.

So instead of sending something readable,
like the recipe for

peanut butter and jelly sandwich,
we have to center something like this.

In reality this process is
a little more complicated.

Our CPU is constantly taking
instructions and executing them,

these instructions are written in binary.

But how do they travel
around the computer?

In our computer, we have something
called the external data bus or EDB.

It's nothing like a bus at all, it's a row
of wires that interconnect the parts of

our computer,
kind of like the veins in our body.

When you send a voltage
to one of the wires,

we say the state of the wire
is on are represented by a 1,

if there's no voltage then we say that
the state is off represented by a 0.

This is how we send around our 1's and
0's, sound familiar?

In the last lesson, we talked about how
transistors help us to send voltages.

Now we know how our bits physically
travel around the computer,

the EDB comes in different sizes,
a bit, 16-bit, 32, even 64.

Can you imagine if you had 64 wires going
you can move around a lot more data right

now we're just going to stick with using
an EDB with 8-bits in our examples,

sending one byte at a time.

Okay, so now our CPU is receiving
a byte and it needs to get to work.

Inside the CPU,
there are components known as registers,

they let us store the data
that our CPU works with.

If for example our CPU wanted to add
two numbers, one number would be

stored in a register A, another
number will be stored in register B,

the result of those two numbers
will be stored in register C.

Imagine the register is one
of our chefs work tables,

since she has a place to work,
she can start to cook, to do so she uses

a translation book to translate her
binary into tasks that she can perform.

Let's jump back for a second.

Remember that our programs are copied
into RAM for the CPU to read,

RAM is memory that's randomly accessed
allowing our CPU to read from

any part of RAM as quickly
as any other part.

We don't actually send data
from RAM over the EDB,

there would be way too much stuff.

RAM can hold millions even
billions of rows of data.

Despite our sandwich example,
most of our recipes aren't simple at all.

There can be thousands of lines long,
we want to process them and

we don't actually go in
any particular order.

Since we can only send one line of
data through the EDB at a time we need

the help of another component,
the memory controller chip or MCC.

The MCC is a bridge between the CPU and
the RAM.

You can think of it like a nerve in
your brain connecting to your memories,

the CPU talks to the MCC and
says hey I need the instructions for

step number three of this recipe,
the MCC finds instructions for

step number three in RAM, grabs
the data and sends it through the EDB.

There's another bus that's
nothing like a bus involved

in the process called the address bus,
it connects the CPU to the MCC and

sends over the location of the data but
not the data itself, then the MCC takes

the address and looks for the data and
then data is then sent over the EDB.

Believe it or not, RAM isn't the fastest
way we can get more data to our CPU for

processing.

The CPU also uses
something known as cache.

Cache is smaller than RAM but

it lets us store data that we use often
and let's just quickly reference it.

Think of RAM like a refrigerator full
of food, it's easy to get into but

it takes time to get something out, on the
flip side of that, cache is like the stuff

we have in our pockets, it's used to store
recently or frequently accessed data.

There are three different cash
levels in a CPU, L1, L2 and L3.

L1 is the smallest and fastest cache.

So now we understand how our
RAM interacts with our CPU but

how does our CPU know when a set of
instructions end and a new one begins?

Our CPU has an internal clock that
keeps its operations in sync.

It connects to a special
wire called a clock wire.

When you send or receive data, it sends a
voltage to that clock wire to let the CPU

know it can start doing calculations.

Think of our clock wires as
the ticking of a clock, for

every tick the CPU does
one cycle of operations.

When you send a voltage to the clock
wire as referred to as a clock cycle,

if you have lots of data you need to
process in the command you need to run

lots of clock cycles.

Have you ever seen a CPU in the store and
has something labeled 3.4 Ghz?

This number refers to the clock speed
of the CPU, which is the maximum

number of clock cycles that it can
handle in a certain time period.

3.40 GHz is 3.4 billion cycles per second,
that's super fast.

But just because it can run at
this speed doesn't mean it does,

it just means that it can't
exceed this number, still,

that number doesn't stop
some people from trying.

There's a way you can exceed the number
of clock cycles on your CPU on almost any

device, it's referred
to as over clocking and

it increases the rate of your CPU clock
cycles in order to perform more tasks.

This is commonly used to increase
the performance in low end CPUs, let's say

you're a gamer and you want to have better
graphics and less lag while playing,

you might want to over clock
your CPU when you play the game.

But there are cons to doing this like
potentially overheating your CPU.