It's from Futuremark, the people that create all the 3dMark programs to benchmark PCs. Find the GTA IV game in there and it will benchmark your PC to tell you if you meet the min. requirements, exceed the requirements or if you are too underpowered to run it.
Also, please do a search next time. This question is ALWAYS being asked at LEAST once a day here. If I received a penny for every time this question was asked, I'd be a millionaire by now!