When reading and decoding sector 0, then sector 8 passes by, so that sector 1, the next sector likely to be needed, will be available without waiting. When reading sector 7, two unneeded sectors, f and 0, pass by before sector 8 is available, and when reading sector 15, the drive will always have to wait an extra revolution for sector 0 on the same track. However, the sector 0 actually needed in most cases will be on the next-higher track, and that track can be arranged relative to the last one to allow the needed time to decode the just-read sector and move the head before sector 0 comes around.