  Quantum information processing and its associated technologies has reached an
interesting and timely stage in their development where many different
experiments have been performed establishing the basic building blocks. The
challenge moving forward is to scale up to larger sized quantum machines
capable of performing tasks not possible today. This raises a number of
interesting questions like: How big will these machines need to be? how many
resources will they consume? This needs to be urgently addressed. Here we
estimate the resources required to execute Shor's factoring algorithm on a
distributed atom-optics quantum computer architecture. We determine the runtime
and requisite size of the quantum computer as a function of the problem size
and physical error rate. Our results suggest that once experimental accuracy
reaches levels below the fault-tolerant threshold, further optimisation of
computational performance and resources is largely an issue of how the
algorithm and circuits are implemented, rather than the physical quantum
hardware
