In the mid-1970s, XMODEM was a simple file transfer protocol developed by Ward Christensen for personal use in his 1977 MODEMASM terminal program. However, because it was so easy to implement, XMODEM became a “hit” in the early Bulletin Board System (BBS). The down side was that XMODEM was very inefficient. Therefore, as modem speeds increased, XMODEM was continually amended to improve performance or to find solutions for other protocol problems. Chuck Forsberg later collected a number of these improvements into his YMODEM protocol, which continued to evolve and led to the eventual demise of the earlier XMODEM versions by the early 1990s.

See Also: YMODEM.