95% is installed. For example, I have Fallout 3 and Oblivion installed and remembered Morrowind so it got tossed in there. Upon inspection, Morrowind is not on the drive atm. Same for Hitman; have Blood Money installed but the other parts aren't.
But yeah, for the most part it's all on there. Kinda forgot the objective and started compiling a full list.
Used to have it on 2x250GB RAID, but moved everything to single 640GB when space ran out. I just can't get myself to uninstall favorites, even though most the time I need to reinstall after new OS anyway.
(currently 469GB worth of game installs)
Got into PC gaming fairly recently, never could afford it in the past. Went a little nuts building a collection over the last 3-4 years.