My son is wondering if his 8GB iPhone 4s will run or install? I think I read somewhere it needs 5.7 GB free space in order to install it. But does it keep using that much or does it release the memory? He realizes it might slow his device down but he wants to try. I told him I would check on here first. I know it will run on my iPhone 6 plus coming...so no problem for me....but I feel bad for my son if he will not be able to run it.