CPP GMR heads do not include a tunnel barrier and, except for the direction of current flow, are similar in operation to the earlier current-in-plane (CIP) GMR devices. Since CPP GMR heads operate with a metallic conducting path, they have a resistance that has typically been far too low. In this case, however, scaling to smaller devices helps by bringing the resistance up to a more manageable level. CPP GMR and CPP TMR devices were originally separated by many orders of magnitude in device resistance. However, intense research on both options has resulted in a rapid convergence such that the devices now differ only by one order of magnitude of resistance and are currently both well within the regime where a practical system can be built.