Yes, I don't believe a concrete computer can "simulate" anything in the relevant sense, let alone a human brain. Computer, as defined abstractly, is just any a

Yes, I don't believe a concrete computer can "simulate" anything in the relevant sense, let alone a human brain. Computer, as defined abstractly, is just any abstract function from {0,1}^N->{0,1}^M. Any realisation of that, eg., by providing each {0,1} as an electrical switch, realises physical properties associated with electrical switches only. The reason that electrical computers are useful has vastly more to do with the electrical part than the computer part. The "computational properties" of the electrical devices we call computers are relatively trivial. But in any case, no system in virute of being an implementation of a discete function thereby acquires physical properties. A woodern "comptuer" is useless precisely because you can't play video games on it. Likewise, even if the brain can be described by a discrete function -- (which is so implausible as to be a bit mad and certainly purely an act of faith) -- then it still requires the relevant physical properties to implement. These properties are extremely unlikely to be those of electrical switches. The "computational work" done by biochemical signalling alone should probably be regarded as "infinite", saying much about the limitations of discrete conceptions of information.