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What Is a CPU?

What is a CPU?

A central processing unit (CPU) is one of the most important parts of any computer. Often referred to as "a computer's brain," it processes and executes our commands and plays a big role in a device's speed and efficiency.

As a developer, understanding how the CPU works can help with debugging and troubleshooting, along with understanding and improving your software's performance.

Ahead, we'll explore what CPUs are used for, their underlying components, and how they work with other parts of a computer's architecture.

The basics of the CPU

The CPU is a hardware component found in the circuit board of your computer or smart device. It looks like a tiny silicon chip, but it has enormous computing power thanks to its built-in transistors, which hold sequences of binary numbers that act as a logic gate.

The CPU is found near the graphics chip and physical memory in a traditional computer. In wearable devices with limited space, manufacturers may use a system on chip (SOC) instead. The SOC combines the CPU with other key components to make them easier to insert into a small space.

You can also find CPUs built into virtual machines. Virtual machines use software called hypervisors to create CPUs, memory, and other components needed to process computing commands.

CPU components

Several major components make up the CPU, including:

  • Control unit (CU): Circuits that direct the memory, logic units, and output of devices by sending out control signals that dictate what each component must do.
  • Arithmetic logic unit (ALU): A circuit that performs calculations while the address computation unit calculates where certain information is stored in the computer's main memory.
  • Memory management unit (MMU): A component that allocates memory for every program and manages the system's RAM, cache, and resources for objects and data structures.

Every CPU also has a cache of reserved memory built into the computer, enabling it to perform commands quickly without pulling memory from the main data storage area. Because the CPU cache is located next to the processor core, memory can be retrieved quickly — but only a limited amount is in the cache.

This cache stores copies of information used during the current session to make tasks faster and simpler to complete. Within the CPU cache, there can be multiple layers, with level one typically a split level and level two acting as a place for information from level one to move when full.

What does the CPU do?

Often compared to a calculator, the CPU does basic computations that allow the computer to respond to your commands. Every CPU has a set of built-in commands known as the instruction set. These basic tasks are hardwired into the CPU and include things like simple mathematical calculations.

CPUs only understand binary code, so software need to translate commands into a series of simple binary codes that the CPU understands. Complex instructions are broken down into simpler tasks that the CPU can complete using knowledge stored in the instruction set. Then, each binary code goes through a series of three steps known as the instruction cycle:

  1. Fetch: In this step, the CPU fetches the command from the computer's RAM (random access memory).
  2. Decode: The CPU calculates what's needed to make the command happen.
  3. Execute: The CPU executes the actions needed to complete the command.

Once the process is concluded, the CPU automatically moves to the next task in the queue and begins the instruction cycle again from the first step.

Your computer's processing speed and response time depend greatly on the CPU. Still, they can also be influenced by memory, core processing power, and other factors.

What is CPU Clock Rate?

The clock speed of a CPU is an important part of how it works and ensures the consistent operation of the computer.

The clock signal tells the CPU to restart its sequence of processing operations. A computer with a faster clock rate restarts the sequence more often, making the CPU work faster and leading to faster operations.

Still, the clock rate has to match the CPU's operations to work properly, so simply setting the clock signal to repeat often won't make it work faster.

For the computer to function, the CPU must complete a cycle and send all the signals needed to complete an operation before the clock signal is sent again to restart the cycle. In more complex CPUs, multiple clock signals might be put in place. This ensures the CPU stays synchronized and completes the full sequence.

Other components used with the CPU

Modern computers have at least two cores operating together to keep up with the number of operations being run at the same time. Some have as many as 24 cores in high-speed processors. This is sometimes called a multicore processor.

These processors, along with the CPU, are capable of performing what's known as multithreading. This is where the CPU essentially creates two virtual cores that are capable of performing tasks and running operating systems separately, giving the same effect as a multicore processor.

While the CPU is a major player in the computer's processing speed, it's not the only factor. Another important factor is the amount of available RAM. RAM powers the applications that the computer uses by providing the short-term memory needed to run them.

RAM is much faster to access than other types of storage on your computer. The data saved is stored while the computer is in use and is erased when the computer is turned off.

In computers with insufficient RAM, when the CPU tries to send a command to be processed, the processing time is much slower as it has to retrieve available memory from another source.

Without a functioning CPU, a computer or smart device can't interpret and execute the commands a user inputs. So, understanding how this component and other key hardware pieces work is a fundamental part of learning about systems operations and computer programming.

Wanna learn more about how computers work? Check out our courses on data structures and computer architecture.


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Computer Science, often referred to as “CS,” is a broad term that covers many sub-disciplines, including the worlds of software *and* hardware. It can be found in every piece of technology you use, from a smartphone or gaming console to a car or ATM. With so many applications for Computer Science, t…

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What Is a CPU?
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