[hamei]

To clarify this a bit, since it's been years and I had to go check :

Display Postscript is an extension to X-Window. Postscript is a complete language, commonly used for printers but can do a lot of other stuff as well. Display Postscript was created to display PostScript commands via an X server. There are advantages to that which I'll skip over.

Most of the Unix licensees used Display Postscript in their window systems. Sun, IBM, and SGI for sure, also possibly HP. 

At some point Adobe pulled the Display Postscript licenses from everyone. Would be interesting to find out why, possibly because of some connection to NeXTStep and Jobs and Apple, which even now ? uses a castrated version, should call it Display PDF

At that point Adobe had to come out with a fix for all the programs, many of them their own, which depended on Display Postscript for on-screen display. The answer was DPSNX - DPS for display postscript, the X for X window, and who knows the n, maybe network ? It was originally DPS/NX.

DPSNX is a client library distributed by Adobe so their applications can still run (Apple would have just told their customers to "fuck off, this is deprecated". Olde Wayes and Olde Dayes was goode). DPSNX works for some Adobe programs and some other programs, if they use the correct version of the client library and if the developers of said programs didn't link to the wrong dpsnx or even exit the program if the one they wanted wasn't found and if a whole bunch of other stuff.

Most of this stuff doesn't matter nowadays because there's not much of anything that depends on Display Postscript and 98% of you don't use these programs anyhow. But the underlying situation is, if your system has the Display Postscript extensions to X, which Irix prior to 6.5.24 ? does, then dpsnx is not only unnecessary but can actually be a problem for programs that don't want it and can't use it, but find it in their path instead of the Real Thing™.

End of history lesson, now robespierre can come correct me :-)