system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What's the difference between CPU and GPU? I know that one is usually for graphics and the other for all the other computations but why you can't use one for the other when they are both logical circuitry?

What makes the difference between them physically? Today a lot of AI works are using GPU, why use GPU if the one for processing things is the CPU? Why miners like GPU more than CPU?
gpt
To put it as simply as possible: a CPU is really really good at doing a lot of different kinds of things one or two at a time, while a GPU is better at doing a few things but a lot of them at one time.

In more detail:
CPU's can be programmed to do addition, subtraction, division, multiplication, and complex logic like 'if A = 1 then B = 2, but if A= 2 and C = 0 then B = 3' and so on. CPU's also have special instructions in them to make certain things faster, like watching video, zipping a file, encrypting your data, lots of special enhancements for very complex math things on top of being very adaptable to random problems you throw at them. A GPU will usually understand fewer instructions but is really good doing a lot of them all at once, like performing lots of addition problems simultaneously. Say you needed to count to 10 a million times, the GPU can do that 1-2-3-4-5-6-7-8-9-10 count by a million all at once taking no longer than counting it just one time, but a cpu would need to count to 10, then start over and count to 10, then start over and count to 10, and on and on a million times over.

Stuff like AI is better on the GPU because it's trying to find the best solution to a problem by running through the problem thousands and thousands of times over and the GPU can do those thousands of runs of thousands of different solutions in really big batches all at once, the CPU would have to do a few at a time for a very long time. Modern GPUs even have special little cores that do certain maths *very* well, the kind of maths you need to use for good AI, and can so it can do lots of those problems all at once even better than older GPUs (pre-RTX) could have done. A CPU is also built to handle lots of tasks related to running the computer as a whole, like talking to your hard drive / ssd, putting data in and out of RAM, keeping programs from interfering with each other, coordinating the hardware on your motherboard so everything plays nice together, lots of important tasks for which GPUs simply do not have the ability to deal with because they weren't built with it in mind.

For a long while now CPU's have been increasingly built to do more things at once, but it's not so easy to write software to take advantage of this and not all software *needs* to do a lot of things at once, so being able to do one thing really fast is a key factor for a good CPU. This is all really simplifying it, but that's the basic difference between a CPU and a GPU, the kinds of instructions they understand and doing things in order vs doing them all at once.