2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/89684We introduce a model of computation based on read only memory (ROM), which allows us to compare the space-efficiency of reversible, error-free classical computation with reversible, error-free quantum computation. We show that a ROM-based quantum computer with one writable qubit is universal, whilst two writable bits are required for a universal classical ROM-based computer. We also comment on the time-efficiency advantages of quantum computation within this model.12 pages, 3 figures, minor corrections + section 5 substantially changedQuantum Physicstext