Earlier quoted context omitted.
In this context what does differentiable mean?
I think the easiest way to see this is by an example of a non-differentable architecture. Let's suppose on the current training input, the network produces some output that is a little wrong. It produced this output by reading a value v at location x of memory. In other words, output = v = mem[x] It could be wrong because the value in memory should have been something else. In this case, you can propagate the gradien…
As for "digital" computers remember they are built out of noisy physical systems. Any bit in the CPU is actually a range of voltages that we squash into the abstract concept of binary.