Basically how fast a neuron can transmit a signal by how many dendrite-to-neuron connections there are.

The funny part is in the human brain, storage and processing are pretty much the same thing (so storage and processing are the same); it'd be like if the whole hard drive was stored in L1 caching. Previously, I had been watching HDD's, wondering when they'd hit the 5 exa- threshold; this article about processors hitting exabytes completely blindsided me, because if its actively processing, it can effectively count as storage, like the brain does it of the two being synonymous - meaning I was expecting this point maybe a decade and a half from now; not potentially next or even this year. Thing is, with a 5 exaflop computer, you could actually do a full human brain. With 64 exa- well... you're solidly into territory where we better start looking to science fiction for advice.