How does processor work? Understanding CPU made easy
How does a processor work? Discover how CPUs execute instructions, and understand cores, threads, cache, GHz and the difference between CPU and GPU.
COMPUTER SCIENCE
Lucas GRANDIER
9/27/20266 min read
If you want to better understand how a computer works overall, check out our article How does a computer work?
Every time you open an application, browse the web, watch a video or launch a game, your computer has to process a huge number of instructions.
At the center of this process is the processor, also called the CPU (Central Processing Unit).
But how does a processor actually work? What are its cores, threads and cache used for? And what does a frequency such as 4 GHz really mean?
Let's take a closer look at how a processor works, step by step.
1. What is a processor?
The processor, or CPU, is one of the main components of a computer.
Its role is to execute the instructions provided by software. It performs calculations, processes data and coordinates many of the operations carried out by the computer.
For example, when you open a web browser, the processor executes the instructions required to launch the program, process data and communicate with other components such as RAM, storage and peripherals.
A processor does not work alone. It constantly exchanges data with the other components of the computer.
2. What is a processor made of?
A modern processor contains billions of transistors, as well as several components responsible for processing and managing instructions.
Transistors
Transistors are the basic building blocks of a processor.
They act as tiny electronic switches that can represent and manipulate binary information: 0 and 1.
By combining billions of transistors, manufacturers can create increasingly complex circuits capable of performing calculations and processing instructions.
Control unit
The control unit interprets instructions and determines which operations need to be performed.
It coordinates the work of the different parts of the processor so that instructions are executed in the correct order.
Arithmetic and logic units
The processor also contains arithmetic and logic units, commonly known as ALUs.
They perform operations such as:
additions and subtractions,
comparisons,
logical operations,
and other calculations required by programs.
Registers and cache
The processor also uses very fast memory areas called registers.
Registers temporarily store data and instructions that the CPU needs immediately.
The processor also has cache memory, which stores frequently used data and instructions so they can be accessed more quickly than from RAM.
3. How does a processor execute an instruction?
To execute a program, the processor repeatedly performs a sequence of operations.
This process is often described using three main stages:
1. Fetch: retrieve the instruction
First, the processor retrieves the next instruction that needs to be executed.
The instruction is generally loaded from memory, and the processor uses information such as the program counter to determine which instruction comes next.
2. Decode: understand the instruction
The processor then decodes the instruction.
In other words, it determines what the instruction means and which operation needs to be performed.
For example, an instruction may tell the processor to add two values, compare two numbers or move data from one location to another.
3. Execute: perform the operation
The processor then performs the requested operation.
An arithmetic or logical unit may perform a calculation, while other parts of the CPU handle data movement or other operations.
The result can then be stored in a register or memory and used by subsequent instructions.
Modern processors make this process much more sophisticated. They can use techniques such as instruction pipelines, branch prediction and multiple execution units to process several operations efficiently.
4. What are CPU cores and threads?
A modern processor can contain several cores.
Each core is a physical processing unit capable of executing instructions.
For example, a processor with 8 cores can process work across eight physical processing units.
But you may also see processors described as having 8 cores and 16 threads.
A thread represents an execution flow that the processor can manage. Technologies such as simultaneous multithreading allow a physical core to handle multiple threads.
This means that 8 cores and 16 threads does not mean the processor has 16 physical cores.
Having more cores and threads can be useful when running several applications at the same time or using software capable of distributing its workload across multiple processing units.
5. What is CPU cache used for?
The processor needs data and instructions constantly.
However, accessing the computer's main RAM takes more time than accessing data stored very close to the CPU.
This is why processors use cache memory.
Cache is very fast memory located inside or very close to the processor. It stores data and instructions that the CPU is likely to need soon.
Modern processors generally use several cache levels:
L1 cache: very small but extremely fast.
L2 cache: larger but slightly slower.
L3 cache: larger again and generally shared between several cores.
The closer the memory is to the processor, the faster it can generally be accessed, but the available capacity is also smaller.
6. What does CPU frequency in GHz mean?
When you look at processor specifications, you will often see a frequency expressed in GHz, such as 3.5 GHz or 4.2 GHz.
GHz stands for gigahertz.
1 GHz corresponds to one billion cycles per second.
So, a processor running at 4 GHz operates at around four billion clock cycles per second.
However, this does not mean that it executes exactly four billion instructions every second.
An instruction may require one or several cycles depending on the processor and the operation being performed.
Frequency is therefore only one factor that influences processor performance. Architecture, number of cores, cache, instructions per cycle and many other characteristics also matter.
This is why a newer processor running at a lower frequency can sometimes be faster than an older processor with a higher clock speed.
7. CPU vs GPU
The CPU and GPU are both processors, but they are designed for different types of workloads.
The CPU is designed to be versatile. It can handle many different types of instructions and tasks.
The GPU, or Graphics Processing Unit, is designed to perform a large number of calculations in parallel.
This makes GPUs particularly useful for:
rendering graphics
video processing
scientific calculations
machine learning
A computer therefore does not choose between a CPU and a GPU. In many cases, they work together, with each component handling the tasks it is best suited for.
FAQs: What to Know About CPU
1. What is a CPU?
The CPU, or Central Processing Unit, is the main processor of a computer. It executes instructions provided by software and performs calculations and data processing.
2. What does GHz mean for a processor?
GHz measures the processor's clock frequency. One GHz corresponds to one billion clock cycles per second. However, frequency alone does not determine processor performance.
3. What is the difference between a core and a thread?
A core is a physical processing unit inside the CPU. A thread represents an execution flow that the processor can manage. A processor with 8 cores and 16 threads therefore does not have 16 physical cores.
4. What is CPU cache used for?
Cache is very fast memory located inside or close to the processor. It temporarily stores frequently used data and instructions so the CPU can access them more quickly.
5. Does a higher GHz always mean a faster processor?
No. Clock frequency is only one factor. Processor architecture, the number of cores, cache size and other characteristics also affect performance.
6. What is the difference between a CPU and a GPU?
A CPU is designed to handle a wide variety of tasks, while a GPU is particularly suited to performing many similar calculations in parallel. They often work together in modern computers.
Conclusion
The processor is at the heart of how a computer works. It executes software instructions, performs calculations and coordinates many of the system's operations.
To understand processor performance, several factors need to be considered: the number of cores, threads, cache memory and clock frequency. However, none of these characteristics alone is enough to determine how powerful a processor is.
In short, the CPU transforms software instructions into operations that the computer can execute. This process, based on billions of transistors and constantly repeated instruction cycles, is what allows our computers to run the applications we use every day.
To go further and understand how the CPU, RAM, SSD and other components work together, check out our article How Does a Computer Work?, which provides an overview of how a computer works as a whole.
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