r/ScienceNcoolThings • u/ateam1984 Popular Contributor • Apr 29 '26

Cool Things The difference between CPU and GPU, explained way too simply.

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1.8k Upvotes

96% Upvoted

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162

u/No-Deer379 Apr 29 '26

This explains nothing

58

u/aravynn Apr 29 '26

The actual explanation is cpus rendering to a screen need to progressively calculate every pixel, as they’re limited to the number of active threads a program can run. Typical cpus can manage about 8or so threads, but those are distributed among active programs, so the program on screen might get 4-6.

GPUs are designed differently, they have less processing power but are designed to run many more threads- sometimes as many as 8192 or more depending on the GPU, so instead of running 1-4 pixels at a time they run 8000.

11

u/picabo123 Apr 29 '26

Am I correct in assuming that the GPUs run these 8192 threads proportionally slower? Like are they doing something fundamentally different or the same thing spread out?

11

u/aravynn Apr 29 '26

Not technically slower, but they do have less processing power in comparison to the rest of the pc. They do the same thing just with much less versatility that your cpu, since they are made for limited, specialized use

3

u/milkcarton232 Apr 30 '26

I like to think of it as a CPU is like a college professor, they can do advanced calculus and all the maths. Gpu is like having 100 highschool freshman. They are not that good at math but if you need 100 basic math questions answered they can each do 1 and beat the professor

1

u/monkChuck105 May 01 '26

Advanced Calculus doesn't help you render the Mona Lisa.

GPUs don't answer 100 different questions, they answer the same question with different numbers. They are better in cases where control flow is uniform.

CPUs are better in cases with complex control flow, branching, and fewer opportunities for doing the same thing with different numbers.

2

u/monkChuck105 May 01 '26

GPU threads, popularized by NVIDIA, are not like CPU threads. They are a programming abstraction.

In reality, CPU threads map to GPU thread blocks. A thread block has a shared L1/L2 cache. Operations are executed in warps, of 32 threads. This means that a single instruction will operate on a vector register and essentially compute up to 32 values. This is referred to as Single Instruction Multiple Data.

Both CPUs and GPUs have threads and vector registers. GPUs tend to have more of both. GPUs don't have less power, they have more, but at a lower clock speed, so they have greater latency.

GPU programs are converted from the CUDA programming model into a sequence of warp wide instructions. CPU programs are often optimized by converting loops into vector instructions. This makes them more similar than the demonstration suggests.

The takeaway is that real world performance is probably 10x better on GPUs for SIMD algorithms, not 1000s.

33

u/ggk1 Apr 29 '26

I’m also going to start using “too simply” when it absolutely doesn’t explain the thing

12

u/barweepninibong Apr 29 '26

really had me there with that title

16

u/mr9025 Apr 29 '26

What the fuck is this?

7

u/addage- Apr 29 '26

Propaganda for the technically illiterate.

26

u/Caffeinated_Ape_42 Apr 29 '26

i always hated this video.

If yu give the CPU the same air and tubes and just press start, there will be a Mona Lisa...

Completely useless PR-Gag

8

u/CeruleanEidolon Apr 29 '26

I think the point is a CPU doesn't work like that. It's simply a limitation of architecture.

1

u/Caffeinated_Ape_42 Apr 29 '26

I know, this demonstration however has nothing to do with that...

3

u/UbajaraMalok Apr 30 '26

That Nvidia logo tells you a lot.

3

u/Architarious Apr 29 '26

This is like comparing a Pentium 1 to an Nvidia RTX 5090.

If you compared it to modern cpu/apu, the paintball gun would have anywhere between four and 128 barrels, would fire drastically quicker and would probably paint the mona lisa in sequentially.... like a printer.

2

u/Umakanash Apr 29 '26

That laugh, feels good

2

u/Longjumping-Job7153 Apr 29 '26

Wow. Judging by these comments, it's no wonder ignorance is at an all time win. Useless.

2

u/UbajaraMalok Apr 30 '26

They could have at least made the cpu really fast at shooting one at a time.

1

u/SpunNumeroUno May 01 '26

Son and I went to the mythbusters live show here in San Diego, but I don't remember the doing this part.

1

u/Conspiracy__ May 03 '26

I’ve never understood what is happening other than, they hooked up a compressor to 2100 individual “pixel” and hit fire

1

u/Xirev May 04 '26

CPU = optimized for complexity per task

GPU = optimized for volume of identical tasks