why is speed limited by Apple download on PC

I have an Apple iMac and a HP PC. iTunes download speed is 1/10 the speed on my HP PC versus iMac. Same network, same downloads, same time. I have tied it directly to the speed from iTunes server. There is nothing on PC slowing down. I can download from other services at similar speeds on PC and iMAC. iTunes is the only one that is severally different.