It can write servo tracks (a circular string of sector marks) with much greater precision than a disk drive can.
This is due to the big motors, sensors and cooling systems that would be too bulky and expensive to build into a disk drive.
A servowriter is used to write servo tracks on the disk platters which make up part of the servomechanism that positions the actuator arm.
A servowriter can be split in three major parts: The head needs to fly on the electromagnetic surface of the disk to place the spin up or down.
The gap in the magnet will read or write using the Laplace Force FL = idl^B This computer-storage-related article is a stub.