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In this paper, we mainly discuss the extendability of current perpendicular to plane giant magnetoresistive (CPP-GMR) heads beyond 100 Gbpsi by using micromagnetic simulation and simulation techniques. An area map of CPP-GMR's resistance-area product (RA) and magnetoresistive ratio for several areal densities is made, which suggests that downsizing of a CPP-GMR head does not cause a decrease in output voltage differently from a current in plane GMR (CIP-GMR) head. At this point, a CPP-GMR has the advantage of extendability to a higher areal density over CIP-GMR, and is the major candidate for the next generation. A CIP-GMR seems to have a scalability limit around 100-200 Gbpsi. On the other hand, the area map also suggests that the RA of the CPP-GMR is a more important keyfactor for higher areal density than for CIP-GMR. The CPP-GMR, therefore, requires not only higher MR, but also less RA as areal density gets higher. Tunneling MR (TMR) has exactly the same problem, so CPP-GMR also has many advantages over TMR, with too high an RA. Additionally, we present CPP-GMR films with the potential for around 500 Gbpsi and discuss a suitable read-head structure for CPP-GMR. Micromagnetic simulation results indicate that the read track width will be controlled by a magnetic field due to the sense current of CPP. We will discuss overall studies on scalability of CPP-GMR.