Zmodem

Developed by Chuck Forsberg, Zmodem is a file-transfer protocol that uses cyclical redundancy checks (CRC) to detect errors and is designed to transfer large files. A distinct feature of Zmodem is the capability to resume a download if a connection failure occurs. Zmodem is able to do this because of the block size (512-byte blocks) data is sent. Predecessors to Zmodem are Xmodem and Ymodem.