Unshielded magnetoresistive heads in very high-density recording

Unshielded magnetoresistive (UMR) heads provide very high signal levels and low noise but, because of their relatively large element height and an insensitive "dead zone" at the sensor edges, they have poor resolution. As a consequence, the signal diminishes dramatically as the recorded density increases and may be as much as 30 dB or a factor of 30 down at very high density. Various techniques have been used to increase the resolution and reduce the "peak-to-bandedge" ratio but they all reduce the bandedge signal as well and hence tend to lower the signal-to-noise ratio. We have found that a peak-to-bandedge ratio of more than 30 dB can be equalized and hence the standard UMR described by Hunt can be used to advantage in very high-density recording. This report describes results obtained with a UMR head reproducing 80 kFCI (3150 FC/mm) signals recorded on Kodak Isomax tape. Bandedge signal and low-density distortion were plotted versus bias field. Surprisingly, maximum high-density signal and minimum distortion occur at about the same bias field. Electronic, thermal, and magnetic noise were measured and tape-noise-limited performance was obtained. Equalized signals from a pseudo-random data sequence were examined with a transition interval analyzer as well as by eye pattern photograph. The transitions were well separated, and the eye pattern was well defined in both phase and amplitude.