RECORD HEAD SATURATION AND OVERWRITE PERFORMANCE OF A BAFE FLOPPY DISK DRIVE

Overwrite is a very complex process involving the record head gap, the overwritten old data bit length, and the record current level and rise time. When the record head is saturating, the overwrite is severely degraded. Barium ferrite (BaFe) media seem to be especially prone to exhibit poor overwrite even when the measured coercivity is relatively low. One BaFe floppy disk drive manufacturer has included a separate wide-gap erase head to solve the problem. The low-frequency intrinsic coercivity of the BaFe disk was a nominal 735 Oc and the drive was equipped with a conventional small gap ferrite record head. With the erase head disabled, the maximum 2f/1f overwrite was 34 dB, where 2f indicates a linear density of 40 kFCI. That same BaFe disk was tested in another drive equipped with a Tilted-Sputtered-Sendust (TSS) metal-in-gap head which gave a much higher overwrite of 40 dB. The signal and overwrite vs. record current curves were completely different. The very small BaFe particle and the unoriented coating cause its effective record coercivity to be much higher than the 735-Oe value measured at low frequency. This causes severe saturation in the ferrite record head and leads to poor overwrite performance. The TSS head is not saturated and so gives maximum overwrite and maximum signal with the same record current.