The first widely used file transfer protocol for personal computers, developed by Ward Christensen for CP/M machines. Xmodem programs supported the earlier checksum method and the subsequent CRC method of error detection. Xmodem transmits 128-byte blocks. Xmodem-1K improves speed with 1KB blocks. Xmodem-1K-G transmits without acknowledgment for error-free channels or when modems are self correcting, but transmission is cancelled upon any error.
A public domain file transfer protocol used in asynchronous data communications, XMODEM organizes data into 128-byte blocks and employs a cyclic redundancy check (CRC) for error control. XMODEM was developed by Ward Christensen in 1977 and quickly became popular in the bulletin board system (BBS) community for file downloads. XMODEM has largely been replaced by ZMODEM. See also asynchronous, BBS, block, CRC, error control, Kermit, modem, YMODEM, and ZMODEM.
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. GNU Free Documentation License. XMODEM. Wikipedia Website. http://en.wikipedia.org/wiki/XMODEM.