SGI O2 - antonizoon/antonizoon.github.io GitHub Wiki
Back in the 1990s, Silicon Graphics made the ultimate supercomputer workstations. These powerful beasts could pump out amazing 3D CGI, and were immortalized by it's use in Hollywood (as shown in Jurassic Park's UNIX System...). And yes, SGI IRIX really did have that 3D filesystem UI.
However, while it rested on it's laurels, SGI was quickly getting outpaced by plain ol' PC graphics cards, which were significantly cheaper and held a vibrant game development community.
Nekochan
The most important community to SGI collectors and enthusiasts is Nekochan, which still maintains a repository of good ol' SGI freeware for download, as well as a comprehensive wiki.
SGI O2
The SGI O2 is the best place for a beginner to start, since it has VGA output and other nice modern goodies.
I found one at the scrapyard for just $2, and couldn't resist taking it home to try it out. It was in piss poor condition with paint all over it (and brittle plastic), but at least it booted up.
Hard Drive
The SGI O2 uses a 80-pin SCA SCSI hotswappable Drive, no more than 1" thick.
Nowadays, even the largest and fastest 300GB 15K SCSI Drives are dirt cheap at $10-20 apiece. Just go to the SCSI drive list and check for the model number on eBay.
If you're not keen on installing IRIX again, or don't know which SCA SCSI Drive to look for, you can buy pre-loaded IRIX 6.5 hard drives from this eBay seller.
Disc Drive
The default Toshiba XM-5701B SCSI CD-ROM Drive was infamous for spitting a small plastic cog out, and refusing to open.
It's possible to fix it, but you're better off replacing it with the Toshiba SD-M1401 SCSI DVD-ROM drive (common drive used on O2+). The Toshiba SCSI Disc Drives are the only ones known to have the correct lip to fit the O2's drive cover.
Unfortunately, these are rare and cost a huge amount of money, so you'll probably want to get an External SCSI CD Drive instead.
There's a Disc Drive replacement guide at the bottom of this guide.
Installing IRIX 6.5
You'll probably want to reinstall IRIX 6.5 from scratch, especially since it's a must if you're installing a new hard drive. You can probably find the discs on eBay for around $40, or burn the discs from torrents.