all the sectors on a disk platter that can be read without moving the head constitute a track.
磁盘盘片在无需移动磁头的前提下即可读取的所有扇区组成一个磁道。
this is due to how websphere mq accesses the disk: essentially, mq can only respond to the commit() when the relevant part of the disk platter has spun past the drive head.