Is the desktop using Windows? Is this a recent issue? When I was using a Windows XP desktop computer it always had slower speeds than the Macs, iPhone and iPad, in spite of all them being on Wifi and the desktop by wire LAN. The ISP technician blamed on the OS, and truth is that no matter what I did, the damn thing was always slower, even after making a clean install and making sure there wasn't any malwares working. If you're on Windows check that.