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XMODEM
Communication protocol
Purpose
file transfer protocol
Developer(s)
Ward Christensen[1][2]
Introduction
1977; 47 years ago (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]
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. Christensen believed his original XMODEM to be "the single most modified program in computing history".[4]
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
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...
of the original XMODEM. YMODEM extended XMODEM in three ways, combining features found in other extended XMODEM varieties. Like XMODEM-CRC, YMODEM replaced...
was not directly based on, nor compatible with, the seminal XMODEM. Many variants of XMODEM had been developed in order to address one or more of its shortcomings...
BRM-1K, see BMP-1 variants HH-1K, see Bell UH-1 Iroquois variants XMODEM-1K, a model of XMODEM YMODEM-1K, a model of YMODEM GSXR 1K, or Suzuki GSX-R1000 Typ...
many protocols of the era, MEGAlink is an expanded version of the seminal XMODEM. While it was a relatively simple and high-performance system, it remains...
Glass (1988) p. 87 Glass (1988) p. 89 Boswell, Peter (2007) [1986]. How XModem, XModem CRC, and WXModem work. Archived from the original on 23 September 2014...
peripheral devices such as USB flash drives Dial-up modems null modem links used XMODEM, YMODEM, ZMODEM and similar File sharing Managed file transfer Peer-to-peer...
the source code. When he needed to send files to Randy Suess, he wrote XMODEM. Jerry Pournelle wrote in 1983 of a collection of CP/M public-domain software...
as a way of improving efficiency compared to non-windowed protocols like XMODEM. See also SEAlink. Conceptually, each portion of the transmission (packets...
VT200/VT300 emulation. Tek4010 emulation. File transfer protocols (Kermit, XMODEM, YMODEM, ZMODEM, B-PLUS and Quick-VAN). Scripts using the "Tera Term Language"...
Display: Minitel, Viewdata, VT100, VT52 File transfer: ASCII, Kermit, XMODEM, YMODEM/YMODEM-G, and ZMODEM List of terminal emulators Official website...
System (CBBS). This used an early file transfer protocol (MODEM, later XMODEM) to send binary files via a hardware modem, accessible by another modem...
and forwarded to (or polled by) another nearby node or hub via a dialup Xmodem session. Messages would be relayed around various FidoNet hubs until they...
and a pty interface on *nix. File transfer options include the ZMODEM, XMODEM and YMODEM transfer protocols (using parts of SEXYZ.) SyncDraw is an ANSI...
SEAlink is a file transfer protocol that is backward compatible with XMODEM but features a sliding window system for improved throughput. SEAlink was written...
4 to 33.6 kilobit dialup modem connections and terminal protocols like XMODEM to the server storage. Before the Web was developed, images would primarily...
file's name, and optionally date and time, since Ward Christensen designed XMODEM to start at block 1, leaving block 0 available. Christensen suggested Forsberg...
terminator. Some data transfer protocols such as ANPA-1312, Kermit, and XMODEM do make extensive use of SOH, STX, ETX, EOT, ACK, NAK and SYN for purposes...
character set. Supported file transfer protocols ranged from Kermit and Xmodem to Ymodem (Batch, 4K and G) and Zmodem (Batch Selections). One feature of...
AppleTalk, a modem or any variety of other connections, transfer files using XMODEM, Kermit or other file transfer protocols, and provide DEC VT102, VT220,...
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