The document discusses the universal Turing machine (UTM), which was developed to address a drawback of the Turing machine. Specifically, with a Turing machine a new machine had to be constructed for each new computation, whereas the UTM is a single machine that can simulate any Turing machine on any input. The UTM works by changing its state based on three bits of information: the description of the Turing machine being simulated, the contents of that machine's tape, and its internal state.