The TCP/IP stack is responsible for the "chopping up" into packets of the data for transmission and for their acknowledgment. Depending on the transport protocol that is used (TCP or UDP) each packet will be acknowledged or not, respectively.
the strategy when the file is chopped up into packets, which are individually acknowledged by the receiver, but the file transfer as a whole is not acknowledged is OK in situations (Applications) that do not need the whole file to be sent, Web site for example: different parts of the web site can arrive in different times.
The other strategy, in which the packets are not acknowledged individually, but the entire file is acknowledged when it arrives is suitable for FTP (mail transfer), we need whole mail, not parts of it.
