Tasks I get for my NVIDIA GPU either run in OpenCL or cuda. Each of the cuda applications has a number after it like cuda45, cuda50, or cuda65 (there might be a few more). What do these numbers mean? I've also noticed that my GPU runs hotter on applications that use cuda65 than ones that run on cuda45.

CUDA is Nvidia's "compute platform". The most recent version is 6.5, but the earlier ones are still in use.
https://developer.nvidia.com/about-cuda

I don't think the later versions necessarily use more power (run hotter), it just depends on the application and the data fed to it.

In cases like GPUGrid, they tend to use the latest version of CUDA utilizing the additional features in those versions. This will typically run your card hotter, but as mentioned above, it comes down to the app.

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The number behind the applications is the version of CUDA this application is built against/optimized for. Not all GPUs know how to utilize all code of CUDA 6.5, thus not all Nvidia GPUs can run applications built with CUDA 6.5
(There's even a whole range of Nvidia GPUs that really cannot use CUDA 6.5 at all). These cards require the use of earlier CUDA versions.

And while older cards can run lots of these newer CUDA versions, they won't completely utilize the possibilities built into these CUDA versions, because their hardware isn't capable of executing the newer commands. You can compare this to a DirectX 9 videocard, which can run DX 10 and 11, but then just uses the DX 9 parts.

The difference between compliant and compatible.

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Ok, so CUDA is like Nvidia's special programming language while OpenCL is more of an open-source thing.

Ok, so CUDA is like Nvidia's special programming language while OpenCL is more of an open-source thing.

That is correct. And nVidia has pretty much dropped development of OpenCL from what I have read.

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