 | This article includes a list of general references, but it lacks sufficient corresponding inline citations. (January 2009) |
| Communication protocol | |
| Purpose | file transfer protocol |
|---|---|
| Developer(s) | Ward Christensen[1][2] |
| Introduction | 1977 |
| Influenced | YMODEM, many others |
| Hardware | modems |
XMODEM is a simple file transfer protocol developed as a quick hack by Ward Christensen for use in his 1977 MODEM.ASM terminal program. It allowed users to transmit files between their computers when both sides used MODEM. Keith Petersen made a minor update to always turn on "quiet mode", and called the result XMODEM.[3][4]
XMODEM, like most file transfer protocols, breaks up the original data into a series of "packets" that are sent to the receiver, along with additional information allowing the receiver to determine whether that packet was correctly received. If an error is detected, the receiver requests that the packet be re-sent. A string of bad packets causes the transfer to abort.
XMODEM became extremely popular in the early bulletin board system (BBS) market, largely because it was 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.[4] Christensen believed his original XMODEM to be "the single most modified program in computing history".[5]
Chuck Forsberg collected a number of common modifications into his YMODEM protocol, but poor implementation led to a further fracturing before they were re-unified by his later ZMODEM protocol. ZMODEM became very popular, but never completely replaced XMODEM in the BBS market.
- ^ Telecommunications: XMODEM: A Standard Is Born, By Alfred Glossbrenner, PC Mag, 17 April 1984, Page 451-452, ... but the protocol itself was long ago placed in the public domain by its creator, Chicagoan Ward Christensen. Since its introduction in 1978, XMODEM ...
- ^ In Focus: History lesson: Ward Christensen's free free-exchange software, By Michael Swaine, InfoWorld, 1 Nov 1982, Page 26
- ^ Ward Christensen, "Memories", 25 November 1992
- ^ a b Meeks, Brock (February 1989). "The ABCs of X-, Y-, and ZMODEM". BYTE. pp. 163–166. Retrieved 2024-10-08.
- ^ "The Virtual Community".