Combinatoric Turing Machines

Combinatoric Turing Machines work on scales of the internet, where there are millions of symbols. Each step in the machine reads and writes millions of symbols. But for efficiency of processing, out of the millions of symbols being read, only a few are chosen to compute the value of a symbol under the read head. Once you have the chosen symbols, you would apply some criteria to chose one: average, max, min, lucky, first, last, sum, best, most terms covered, etc.