Since early 2016, the SGI TechPubs archive is no longer available at SGI.
The documentation is now available at https://techpubs.jurassic.nl/.
(Related forum post: http://forums.nekochan.net/viewtopic.php?f=6&t=16730750)
Another way to access the old SGI documentation is to take their old links and visit them in the Archive.org's Wayback Machine.
Another way to find the required documentation is to search in http://manx.classiccmp.org/mirror/techpubs.sgi.com/.
Some TechPubs documentation can also be found on http://retrogeeks.org/sgi_bookshelves/index.html.
And another index of PDF documentation is at http://www.irix7.com/.