[dchichkov]

They are doing matrix multiplications. To pass input a single time through even some very large neural network - it is a relatively fast operation (if compared to training such a network, that is). Training requires data centers and arrays of GPUs. Passing the input through the network - usually you can get away with a single core and vectorized operations. Unless you are doing high resolution computer vision in real time... You can still get away with the single core even then, but that requires some very smart sublinear processing.

[ibrahima]

Completely right. Applying a neural network is much faster than training one. The main trick here is fitting the trained model into cache (or smaller) so that the matrix multiplies are fast.