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What is the difference between a single processing unit of CPU and single processing unit of GPU? 
Most places I've come along on the internet cover the high level differences between the two. I want to know what instructions can each perform and how fast are they and how are these processing units integrated in the compete architecture?  
It seems like a question with a long answer. So lots of links are fine.   
In the CPU, the FPU runs real number operations. How fast are the same operations being done in each GPU core? If fast then why is it fast?  
I know my question is very generic but my goal is to have such questions answered.

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This are not Real numbers as $\mathbb{R}$, but at this point - CPU has double precision floating point numbers, GPU very low number of units processing them, floats on GPU are halfs.
This is due to graphics (this was the main goal before parallel processing), where results are rounded to display, so speed vs accuracy tradeof went that way.
GPU core frequencies are smaller than CPUs, number of operations is very limited on GPU (boosted by video decoder), and there is a huge difference in branch prediction - CPU has very long and complex prediction, while GPU just recently got it added.

Single core on GPU: it is Streaming Multiprocessor (there are about 4 - 16 per card), it includes cuda cores (which is about 32-64), and they work in lock-step, so it differs from CPU threads (not locked).

It is hard to compare like this, but in short - single core on GPU is still parallel unit working slower than CPU core, less memory, registers and instructions than CPU, with very short branching prediction and preferable half floats, nowadays normal floats but having about one-two processing units for double precision, some time ago integer operations were slower on GPU (not onlu by frequency) - but this changed recently.

The same operation on floats - they are slower on GPU than CPU due to frequency.

You might be interested in AMD architecture, Nvidia architecture and Intel architecture to compare instructions set and hardware differences further.

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A GPU (graphics processing unit) is designed for accelerating images and graphics in computer systems. It's designated in parallel architectures and efficient algorithms with hundreds to thousands of homogeneous cores that speedup data processing (for graphics and images traffic patterns) in parallel and get it done faster and more efficient than a general-purpose CPU. For example, NVidia is one of the leaders in GPU processors manufacturing. As my best knowledge, NVidia has announced its Tesla K40 with 2880-core integrated in a single-chip and these cores are served as specific purposes in graphics processing in parallel.

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To be simpler with the words CPU (central processing unit- a purpose processor) has always been called the brains of the PC. But nowadays, that brain is being improvised by another part of the computer i.e the GPU (graphics processing unit).

Basically GPU's advanced features were only used in 3D and high end gaming. But these days GPU plays a vital role more importantly in speeding up computational workloads. Read more at NVIDIA CEO Jen-Hsun Huang’s latest blog post for more deeper knowledge of GPU.

CPU: it contains fewer number of cores with a lot of cache memory and can handle few threads at a time. whereas GPU has power to handle thousands of threads.A CPU generally has higher operating frequency and is designed for general purpose use and vice versa with GPU.But the combination of both the features will contribute to better performance and efficiency.

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  • $\begingroup$ Link to the post will be better. $\endgroup$ – new-kid Apr 19 '16 at 15:21
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    $\begingroup$ differencebetween.net/technology/difference-between-cpu-and-gpu go through this link for difference and more accurate points $\endgroup$ – Sheetal U Apr 19 '16 at 15:26
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    $\begingroup$ When someone comments on your post, rather than leaving comments with clarifications or additional information, it's better to edit the answer to incorporate that information. We want to build up a repository of high-quality questions and answers; and we want posts to be self-contained (people shouldn't have to read the comments). Comments exist primarily to help you improve your answer. Thank you! $\endgroup$ – D.W. Apr 19 '16 at 18:01

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