GDOS was atari's printer and font management system.
Its quite outdated now, its slow and the drivers are no longer updated (as far as i know)
a lot of programs use GDOS to handle fonts and printing
but some (eg Calamus) have there own ways of doing this (which are considerably quicker)
What i would recomend instead is a recent copy of NVDI
this is GDOS compatible and as well as a much improved font and
printer handling system, it speeds up many aspects of the O/S.
it isnt cheap, but you wont regret spend you money.
RE: GDOS for drivers for SLM804 printer for MEGA S