4Sight
From TechPubs Wiki
4Sight is the windowing system used by 4D1 (the immediate predecessor of IRIX). It is based on the NeWS system produced by Sun Microsystems. It is a stacking windowing system with full IRISGL-type graphical acceleration and effects.
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IRIX 4.x and up uses XSGI, an X11-based windowing system, instead of 4Sight as by this point NeWS was seen as passe due to its slower speed, poor market acceptance and the fact that it required PostScript royalties.