Xmodem

XMODEM

XMODEM is a simple file transfer protocol developed as a quick hack by Ward Christensen for use in his 1977 MODEM.ASM terminal program. XMODEM became extremely popular in the early bulletin board system (BBS) market, largely because it was so simple to implement. It was also fairly inefficient, and as modem speeds increased this problem led to the development of a number of modified versions of XMODEM to improve performance or address other problems with the protocol. Chuck Forsberg collected a number of these into his YMODEM protocol, but poor implementation led to a further fracturing before they were re-unified by his later ZMODEM protocol.