How Do CPUs Work?

Summary

This video explains how CPUs, or central processing units, work by delving into their internal structure and operations. It covers the key components of a CPU, including the control unit, arithmetic logic unit (ALU), and registers, while describing the role of buses for communication. The video also introduces machine code, assembly language, and the fetch-decode-execute cycle, which are essential for CPU functionality. It concludes by discussing modern CPU features such as multiple cores, cache memory, and specialized units for tasks like graphics processing and machine learning.

Takeaways

• 🤖 CPUs are digital machines designed to execute a sequence of instructions, primarily built from millions or billions of transistors.
• 🔧 Most CPUs today follow the von Neumann architecture, which includes a control unit for coordinating activities and an arithmetic logic unit (ALU) for mathematical and logical operations.
• 💾 CPUs constantly exchange data with memory and peripherals using communication channels called buses: the address bus, data bus, and control bus.
• 📚 Registers are small memory banks inside a CPU, used to store data, instructions, or addresses, with sizes varying in modern processors (e.g., 32, 64, 128 bits).
• ⏲️ CPUs operate based on a clock signal, measured in gigahertz, allowing modern CPUs to process billions of instructions per second.
• 🔄 The basic CPU operation is the fetch-decode-execute cycle, where the CPU fetches an instruction from memory, decodes it, executes it, and repeats the cycle.
• 🧮 Assembly language is a human-readable form of machine code that can be used to interact with a CPU, making tasks like adding numbers or moving data between registers easier to understand.
• ⚙️ Modern CPUs are complex, featuring multiple cores that can handle parallel processing, several levels of cache memory, and advanced prediction algorithms for faster data access.
• 🎮 Many modern CPUs also include specialized components like floating point units (FPUs) for precise calculations and graphics processing units (GPUs) for handling media and visual tasks.
• 🧠 Some modern CPUs integrate neural accelerators or intelligent processing units (IPUs) for machine learning tasks, showing how versatile these processors have become.

Q & A

What is a CPU and what role does it play in a computer?

A CPU, or Central Processing Unit, is a single-chip digital machine that executes a sequence of instructions known as a program. It functions as the brain of the computer, coordinating operations and performing mathematical and logical computations.

What is the von Neumann architecture and how does it relate to modern CPUs?

The von Neumann architecture is a computer architecture model that separates data storage and program instructions in memory. Most modern CPUs are based on this architecture, containing a control unit to coordinate operations and an arithmetic logic unit (ALU) to perform calculations.

What are the main internal components of a CPU?

The main internal components of a CPU include the Control Unit, Arithmetic Logic Unit (ALU), and registers, which are small memory banks for storing data, instructions, or memory addresses.

What are registers, and what purpose do they serve within a CPU?

Registers are very small memory banks inside the CPU used to temporarily store data, instructions, or memory addresses during computation. They allow the CPU to access frequently used data quickly.

What are the three types of buses in a CPU and their functions?

The three types of buses in a CPU are: 1) The address bus, which communicates memory addresses to RAM or other components, 2) The data bus, which transfers data values, and 3) The control bus, which exchanges control signals with other components.

What is the fetch-decode-execute cycle in CPU operations?

The fetch-decode-execute cycle is the basic operational process of a CPU, where it first fetches an instruction from memory, decodes it to understand what action to take, and then executes the instruction before moving on to the next one.

What is machine code, and how does it relate to assembly language?

Machine code is the most basic form of programming, consisting of binary numbers that directly control CPU operations. Assembly language is a more human-readable representation of machine code, which is then converted into machine code by a compiler.

How do modern CPUs differ from older CPUs like the Z80?

Modern CPUs are significantly more complex, with multiple cores capable of handling several fetch-decode-execute cycles simultaneously. They also include advanced features such as multiple cache levels, predictive algorithms, and additional components like floating point units and integrated GPUs.

What role does a clock signal play in CPU operations?

A clock signal synchronizes the operations of the CPU, triggering each step of the fetch-decode-execute cycle. Modern CPUs have clock signals measured in gigahertz, enabling them to process billions of instructions per second.

What are some additional components found in modern CPUs, and what are their functions?

Modern CPUs often contain additional components like Floating Point Units (FPUs) for precise mathematical calculations, integrated GPUs for handling graphics, media encoders for video processing, and neural accelerators for machine learning applications.

Outlines

00:00

🔍 Introduction to CPU Operations

The video begins by addressing a common question: How do CPUs (Central Processing Units) work? The host explains that CPUs are digital machines designed to execute sequences of instructions, known as programs. They are constructed from millions or billions of transistors. To understand their functionality, it’s essential to consider their internal structure, often based on the Von Neumann architecture. This architecture features a control unit to coordinate activities and an Arithmetic Logic Unit (ALU) for mathematical and logical operations. The CPU constantly exchanges data with memory and interacts with various peripherals. The speaker draws a personal connection by mentioning the Z80 CPU, which he first programmed in machine code, highlighting that a deep understanding of CPU operations requires knowledge of machine code.

05:00

🖥️ Key CPU Components and Operation

This section discusses the basic internal components of a CPU, using the Z80 CPU as an example. It explains the roles of the control unit and the Arithmetic Logic Unit (ALU) and introduces registers, which are small memory units inside the CPU. Registers can store instructions, data, or memory addresses (also known as 'addresses'). The CPU communicates using three types of buses: the address bus, data bus, and control bus. To execute a program, the CPU relies on a clock signal, which coordinates each step of the 'fetch-decode-execute' cycle. This cycle is critical to understanding how instructions are processed by the CPU.

10:01

📝 The Fetch-Decode-Execute Cycle Explained

This paragraph dives deeper into the 'fetch-decode-execute' cycle, the fundamental operation of all CPUs. It describes how the CPU uses a program counter (instruction pointer) to fetch instructions from memory, decode them, and then execute the corresponding operation. Instructions are binary numbers, and the decode step translates them into specific commands. It also introduces assembly language, a human-readable format that is converted to machine code by a compiler. The example of adding two numbers in memory is given, highlighting how instructions move data between registers, perform arithmetic operations, and write results back to memory.

Keywords

💡CPU (Central Processing Unit)

A CPU, or Central Processing Unit, is the primary component of a computer that executes a sequence of instructions known as a program. It consists of millions or billions of transistors and forms the core of digital computing. In the video, the CPU's role in the von Neumann architecture is explained, emphasizing its importance in processing data, interacting with memory, and communicating with peripherals.

💡Von Neumann Architecture

The von Neumann architecture is a computer design model that consists of a control unit, an arithmetic logic unit (ALU), memory, and input/output peripherals. It allows for the storage of both instructions and data in memory, facilitating the CPU's ability to fetch, decode, and execute instructions. The video mentions that modern CPUs follow this architecture, and it serves as the foundation for understanding how CPUs interact with memory and peripherals.

💡Transistors

Transistors are tiny electronic components that act as switches or amplifiers in digital circuits, making up the fundamental building blocks of CPUs. The video explains that modern CPUs are made up of millions or billions of transistors, which work together to process data and execute instructions efficiently.

💡Arithmetic Logic Unit (ALU)

The Arithmetic Logic Unit (ALU) is a critical part of the CPU that performs arithmetic and logical operations, such as addition, subtraction, and comparisons. The video describes the ALU as essential for executing the mathematical and logical operations required by programs, highlighting its role in modern and older CPUs like the Z80.

💡Registers

Registers are small, high-speed storage locations within the CPU used to store data temporarily during instruction execution. They hold values such as instructions, data, or memory addresses. In the video, registers are discussed in terms of their sizes (e.g., 8-bit, 16-bit, 32-bit) and their importance in processing data in the fetch-decode-execute cycle.

💡Buses

Buses are communication channels within the computer that transfer data, memory addresses, and control signals between the CPU, memory, and other components. The video identifies three key types of buses: the address bus, data bus, and control bus, each playing a specific role in the exchange of information within the CPU.

💡Fetch-Decode-Execute Cycle

The fetch-decode-execute cycle is the basic operational process of a CPU, where it fetches an instruction from memory, decodes it to determine what action is required, and then executes the instruction. The video explains that this cycle is triggered by a clock pulse and repeats continuously to process program instructions.

💡Machine Code

Machine code is the lowest-level programming language, consisting of binary numbers that represent instructions directly executed by the CPU. The video discusses how machine code is used to control individual CPU components and references the Z80 CPU, where machine code programming played a crucial role in early computing.

💡Assembly Language

Assembly language is a low-level programming language that provides a more human-readable form of machine code. It is converted into machine code by a compiler for execution by the CPU. The video illustrates assembly language with an example of how two numbers in memory are added together, highlighting its close connection to CPU operations.

💡Clock Signal

A clock signal is a timing pulse generated by a quartz crystal on the motherboard, used to synchronize the operations of the CPU. The video explains that the clock signal regulates the pace at which the CPU processes instructions, with modern CPUs operating at speeds measured in gigahertz, allowing them to execute billions of instructions per second.

Highlights

Introduction to how CPUs work, focusing on the internal functions of microprocessors.

CPUs are single-chip digital machines for executing a sequence of instructions known as a program.

CPUs are mainly built from millions or billions of transistors and are structured using the Von Neumann architecture.

The CPU architecture includes a control unit to coordinate operations and an arithmetic logic unit (ALU) for performing mathematical and logical functions.

The control unit, ALU, and registers, which are small memory banks, are critical components of a CPU’s operation.

CPUs communicate with memory and other components through three communication channels: address bus, data bus, and control bus.

The fetch-decode-execute cycle is the fundamental operation of a CPU, involving fetching instructions from memory, decoding them, and executing them.

Modern CPUs are extremely fast, processing billions of program instructions per second, aided by a clock signal measured in gigahertz.

The program counter, or instruction pointer, holds the address of the next instruction to be executed.

Assembly language provides a more human-friendly form of machine code, which is compiled into binary instructions that a CPU can process.

Example of assembly language operation: moving values from memory to registers, performing arithmetic, and storing results in memory.

Modern CPUs contain multiple cores, allowing for parallel execution of instructions through independent fetch-decode-execute cycles.

CPUs also include cache memory to store frequently accessed data and predictive algorithms to pre-load data from RAM.

Additional CPU components include floating-point units (FPUs) for advanced mathematical calculations and integrated graphics processing units (GPUs) for display and media encoding.

Advanced CPUs may also feature integrated neural accelerators for machine learning applications, but at the core, CPU operations still revolve around manipulating data and addresses.

Transcripts

[Music]

welcome to another video

from explaining computers

this time i'm going to answer a question

that i'm very frequently asked

which is how do cpus how do central

processing units

actually work so let's go and delve into

the inner functions

of the microprocessor

cpus or central processing units are

single chip digital machines for

executing a sequence of instructions

called a program cpus are mainly built

from millions or billions of miniature

transistors but to understand their

operation

it's best to focus on their internal

structure or architecture

today most cpus form part of a von

neumann architecture

this includes a control unit that

coordinates the processor's activities

as well as an arithmetic logic unit that

performs mathematical and logical

operations as we're about to see cpus in

the von neumann architecture

need to constantly exchange data with a

computer's memory

whilst also interacting with input and

output peripherals

personally whenever i think about cpu

operations

i remember the z80 cpu that was found in

the sinclair zx81

and other early micro computers the zx81

was the first computer i ever owned

and back in the 1980s i learned to

program it z80 cpu

in machine code machine code

is the most basic form of programming as

it takes direct control

of individual cpu components

so if you want to deeply understand how

a cpu works

you need to delve into machine code

here we see the internal architecture of

the z80

modern cpus are far more complicated but

by looking at the z80 we can more easily

highlight

a cpu's basic components

just like in the von neumann block

diagram the z80 has a control unit to

coordinate its operations

as well as an arithmetic logic unit or

alu

there are also a number of registers

which are very small memory banks

just a few bits in size here on the z80

all registers have either an 8 or 16 bit

capacity

although in a modern processor registers

are typically 32

64 80 128 256

or 512 bits in size as we will see in

the next section

registers can be used to store

instructions or data

as well as memory locations which are

known as addresses

in order to interact with the rest of

the computer a cpu

has three communications channels called

buses

firstly we have the address bus which is

used to communicate memory addresses to

ram

or other components secondly there is

the data bus

which is used to communicate data and

finally

there is the control bus which is used

to exchange control signals with other

components

so for example if a cpu needs to read

the value in a particular memory

location

it will use its address bus to

communicate the location address

the control bus to indicate what it

wants to read the data from it

and the data bus to actually transfer

the data value

in order to run programs cpus

rely on a clock signal as is generated

by a clock chip and a quartz crystal

located somewhere on the computer's

motherboard

today clock signals are measured in

gigahertz

with modern cpus able to process

billions of program instructions per

second

the most fundamental aspect of cpu

operation

is the fetch decode instruction cycle

each part of this cycle is triggered by

a clock pulse signal

with the cpu first fetching an

instruction from memory

before decoding it executing it and

moving on

to repeat the process of fetching

decoding

and executing the next instruction and

so on

to keep track of what it's doing and to

perform its work

a cpu relies on several different

registers at the most basic level

there is a program counter also known as

the instruction pointer

which contains the address of the next

instruction to be fetched

when the fetch decode execute cycle

begins the cpu reads the instruction

held at this memory location and stores

it in its instruction register

ready to be decoded and executed

the program counter is also incremented

ready for the next instruction

cycle it's important to appreciate that

in machine code instructions are simply

binary numbers that correspond

to a particular command the decode part

of the fetch decode execute

cycle therefore looks up what command

the value held in the instruction

register

represents many instructions perform

arithmetic or logical operations on one

or more registers

whilst others move data between

registers and memory

or jump to other parts of the program if

certain logical conditions

are met note that here all registers

data values and memory addresses are

illustrated as being eight bits in size

to keep our graphics as clear as

possible

in order to make machine code easier to

write

it is often expressed in a

human-friendly form

known as assembly language this is then

converted into machine code by a program

known as a compiler so it can be run by

a cpu

to provide an example of assembly

language and related cpu operation

let's imagine that we have two numbers

held into consecutive memory addresses

and that we want to add them together

and store the result

in the next memory address assuming that

we already have the memory location of

the first number

stored in register 10 the assembly

language to make this happen

could look something like this

what we see here is a small snippet of

x86 assembly language

in which the registered names are

prefixed by a percent sign and memory

addresses

are contained in brackets what the code

does

is to move the value held at the memory

address stored in register 10

to register 12 to increment the value in

register 10

so that it points to the next memory

address and to move the value

contained at this memory address to

register 13.

the program then adds together the

values held in registers 12 and 13

with the result ending up in register 13

before incrementing the address location

held in register 10 once again

and finally writing the result held in

register 13

back to this memory location note

that in x86 machine code it is possible

to add a register value directly to a

value in a memory location

so this example could be coded in other

ways

and if all of this seems rather tedious

then it very much

is but moving data and addresses

into and out of registers and performing

mathematical and logical operations on

them

or what the inner workings of a cpu are

all about

so far in this video i've simplified

matters as much as possible

with cpu architectures that only include

a handful of registers and other basic

elements

and which execute just one instruction

at a time

however most modern cpus are far more

complex for start

most modern cpus have many cores each of

which can loop through its own

fetch decode execute cycles in order to

allow many instructions to be processed

at the same time in addition modern cpus

contain several levels of cache which is

very fast memory

into which data and instructions are

loaded before being accessed by the rest

of the cpu

modern cpus also contain complex

predictive algorithms that try to

anticipate the memory values that a cpu

is likely to require

so they can be pre-loaded from ram to

cache before they are needed

in addition to their control and

arithmetic logic units

many modern cpus also contain other

components

including a floating point unit or fpu

for carrying out highly accurate

mathematical calculations

also included in most modern cpus are

display

controllers or graphics processing units

as well as media encoders

some modern cpus even have integrated

neural accelerators or intelligent

processing units to assist with machine

learning applications

even so at the most basic level the way

that all cpus work is as previously

described

with data and addresses being loaded

into registers from memory or other

storage

before being subject to mathematical or

logical manipulation

and written back to storage or used to

trigger control

signals

modern microprocessors are some of the

most amazing machines ever

created and have become the bedrock of

human civilization

hopefully in this video i've given you

some idea about how microprocessors

about how

cpus actually work and if you'd like me

to do the same for other computing

components

please let me know down in the comments

section

but now that's it for another video if

you've enjoyed what you see there please

press that like button

if you haven't subscribed please

subscribe and i hope to talk to you

again

very soon

you