Tektronix Phaser 600 - Manual (Page 381)

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If you are using Apple Macintosh QuickDraw GX, use the Phaser 600 GX driver to
print to your Phaser 600 printer.
■ The Phaser 600 GX driver works with QuickDraw GX and
non-QuickDraw GX applications.
■ QuickDraw GX does not work with non-QuickDraw GX printer drivers. If
you want to print from non-QuickDraw GX applications with a driver such
as the LaserWriter 8.x, you must first disable QuickDraw GX; see
Disabling
QuickDraw GX for instructions.