我可以使用HTTP传输的最大文件大小是多少？并使用FTP？

Added: I am conducting a study for a new system we're going to develop in my work. It consists in authenticating users, displaying what files they want to download and downloading them. Also, if the files are not readily available, the user can't download them, but the server obtains a copy of the requested file and notifies the user by mail when he can get the file. We expect files to be tipically from 2 to 50 gigabytes in size, for now.: I am conducting a study for a new system