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How does a CPU Work?

Contel Bradford
Contel Bradford

The Central Processing Unit (CPU), or processor, is a component that acts as the brain of a computer system. Instead of actually thinking, however, it moves data around the system in ways defined by computer programmers. A CPU essentially performs three basic functions. It accepts input, processes data, and provides output. These are critically important to the operation of any computer system.

Input is the process by which external data is entered into a computer. It is mainly provided by common input devices, such as a keyboard, mouse, scanner, or modem. Once the computer analyzes the input, that data is then processed and converted into output.

A dual core CPU mounted to a motherboard.
A dual core CPU mounted to a motherboard.

Output is the end result of the processed data input into the computer system. It refers to a process by which the CPU sends data to installed devices, such as a monitor, printer, or even a running computer program. The output data can either be stored temporarily or permanently, meaning the computer must have a way to contain this data while processing is being performed. This is where memory comes in.

A Central Processing Unit (CPU).
A Central Processing Unit (CPU).

A computer stores data in memory, and retrieves the data it requires from either Read-Only Memory (ROM) or Random Access Memory (RAM). ROM is permanent memory that retains data even when the system is turned off. RAM is temporary memory and, therefore, any data stored there will be deleted when the system is turned off. The CPU uses RAM to store and retrieve data on an as-needed basis. For example, the instructions needed to launch a program would be stored in and retrieved from RAM.

In most cases, a CPU must be connected to a motherboard in order to work properly.
In most cases, a CPU must be connected to a motherboard in order to work properly.

The cache also plays an important role in the functioning of a CPU. A cache is small amount of high-speed memory that holds data. Some processors have a cache that varies in static RAM (SRAM) capacity. SRAM is considerably faster than Dynamic RAM (DRAM), which is designated for the main memory in the computer. The overall purpose of the cache is to increase the speed at which data is processed.

Data requests made by the CPU are handled by a cache controller. This can either be built into the motherboard or the processor itself. Being that cache is an internal component, it can be accessed directly and, therefore, maintain the speed of the processor. Without this component, the computer would run dramatically slower, as the processor would be forced to wait for data to be sent from the main system memory.

The CPU is not only an important element, but a crucial one. Without it, the system would not be able to function at all. This critical component also determines the overall performance any given computer system will provide.

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Discussion Comments


You know, I built my latest computer from scratch and I still don't entirely understand how the CPU works. I do understand that it is the part that processes information, and I have a fairly rough understanding of what kind of CPU I needed to work well with the kind of computer I wanted to build, but I think I would fail any test that happened to cover CPU uses.

I didn't need to know what it did to install the CPU and the fan though. I just needed to know how to follow simple instructions. And people who buy their computer from a store probably don't even need to know that much!


@Fa5t3r - I never really thought about it like that. I wish there was a way to do a CPU upgrade on my brain though! I feel like I probably got an outdated model compared with my friends.

At least with a computer I can replace the parts when they are faulty or when they wear out. Sadly, we can't do the same with our brains.


This can actually make a fairly good analogy for the human brain as well. We have a kind of CPU and long and short term memory and it's good for students, in particular, to know how these work.

Our CPU isn't good for permanent storage, or even short term storage but it is where all the work gets done. It's relatively shallow. So, for example, if a high school student knows their time tables and those are accessible from long term memory, they can work out an algebra equation more efficiently, because they aren't trying to fit that component of it into the CPU at the same time as understanding the mechanics of the equation itself.

Short term memory (the same as RAM) is where we stick all the stuff that we learn, but don't connect to other bits of information. This is why you might learn a whole bunch of facts for a test and then forget them a few months later.

Long term memory (ROM) is where we put things that make sense to us and fit into our other memories. Those stick around for years, if not forever.

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    • A dual core CPU mounted to a motherboard.
      A dual core CPU mounted to a motherboard.
    • A Central Processing Unit (CPU).
      By: Gudellaphoto
      A Central Processing Unit (CPU).
    • In most cases, a CPU must be connected to a motherboard in order to work properly.
      By: Lusoimages
      In most cases, a CPU must be connected to a motherboard in order to work properly.