A method of writing servo patterns on a disc in an external servo track writer
("STW") includes enclosing the disc and an actuator arm within an internal enclosure,
while additionally enclosing the internal enclosure and the remainder of the STW
by an outer cover. The internal enclosure is filled with a low-density gas prior
to writing the servo patterns on the disc. Gas overflowing from the internal enclosure
is contained by the outer cover which further retains the low-density gas once
the internal enclosure is opened at the conclusion of the servo writing process.
The low-density gas is then purged from the STW for recycling before the outer
cover is opened and the disc is removed. The internal enclosure may comprise two
separate components moveable between an open and closed position to allow for loading
and removal of the disc from a spindle motor of the STW.
