They just put the bit about external devices in so that you would be sure that you couldn't, for example, plug in a drive to make the storage bigger or infinite. It make your computer as finite-memory machine.
A Turing machine has an unlimited tape, so your finite-memory computer can't satisfy that. Similarly a pushdown automaton has a potentially-unlimited stack.
However, a computer is fully programmable, while a finite state machine is not. So, while strictly your computer has a finite number of states and well-defined transitions between them (since its memory and CPU together have only finitely many possible states), I would say it is more like a linear bounded automaton.