If you need to ask, I suggest that you re-evaluate your choice.
HIS Digital is basically unbranded. There's probably one or two people here who have heard of them, but not enough people to get a real grasp of the quality of the cards.
As for how much space they take - have a look at the web site, I don't know which model you've bought.
www.hisdigital.comRunning four of them on one mobo without risers? If the cards have any horsepower, then they're going to get pretty toasty. If you don't use risers then you'll probably cook the middle two leading to a very unreliable system.
Sorry to burst your bubble.
