data packet Although your computer and modem can send data one character at a time, when you're surfing the Internet, downloading files, or sending email, it's more efficient to send information in larger blocks called data packets. Modems generally send packets of around 64 characters along with some extras for error checking. When downloading files using a protocol like Xmodem, however, the packets are larger. And when using Internet protocols such as TCP/IP, the packets are larger still--around 1,500 characters. See also: asynchronous communication, TCP/IP, Xmodem