What is zone bit recording?

Zone bit recording(ZBR) stores more than one bit of information in each magnetic domain. When a magnetic domain is magnetized into only one direction, the area represents the value of one bit. When a domain is magnetized in both available magnetic directions, the area can be used to represent 2 bits of information. Some disk drive formats use ZBR on the inner tracks of a disk where sectors are very small. The technique allows the bit pitch to be reduced for higher recording density.