The AMD 6990 has ~1.37TF double precision, but uses 2 GPU chips to do it, where this chip is that perf level.

It is difficult to get good performance out of the GPUs for a very wide range of highly parallel programs. Effectively, you are programming a part that is trying to give you mainly a graphics part, since that is where the volume is, with enough compute compromises to try to grow that market. MIC is designed to be a compute processor from the get go. How about this for a difference: it can boot linux all on its own! You can ssh into it and run programs. You can even run 'reverse offload' programs that call out to code on the CPU! Trying doing any of that with a GPU.

BTW, this MIC chip has a large number of cores (50+), these are real cores, and they're not doing the GPU marketing trick of counting SIMD lanes as "cores". You could multiply 50+ * 16 to get the equivalent number of GPU "cores". Each core is cache coherent, with a decent memory hierarchy designed for compute. There's no graphics tax on here.

I have much more expectation that Intel can leverage their massive process advantage to keep MIC ahead on compute performance each generation. It'll be a relief to have compute parts rather than repurposed GPUs.

x86 instruction set. GPUs are a pain to program and port applications to.

If I recall correctly, this is somewhat of a spinoff of the larrabee chip - http://en.wikipedia.org/wiki/Larrabee_(microarchitecture)

You can see in the wikipedia page the benefits of Larrabee over traditional GPUs. I believe the new chip was designed to be even more flexible and similar to modern processors.

It's x86, a normal Intel CPU. It can even run Linux. Drastically different from what a GPU is

mobility.