ZMODEM - Computer Definition
A public domain file transfer protocol used in asynchronous data communications. ZMODEM offers a number of improvements to the earlier XMODEM protocol, including an expanded 32-bit cyclic redundancy check (CRC) for purposes of improved error control. ZMODEM also supports larger block sizes (512 bytes), allows a transmission to resume where it left off in the event of a communications failure, and reduces latency through a sliding window protocol that allows a modem to transfer a series of blocks without waiting for individual acknowledgements from the receiving modem. ZMODEM was developed by Chuck Forsberg in 1986 for use in the Telenet X.25 network, and quickly became popular in the bulletin board system (BBS) community for file downloads. See also asynchronous, BBS, block, CRC, error control, Kermit, modem, X.25, XMODEM, and YMODEM.
An asynchronous communications protocol providing faster data transfer rates and better error detection than XMODEM. ZMODEM not only supports larger block sizes than XMODEM but also enables the transfer of data to resume where it left off after a communications failure.
Jupitermedia Corporation. ZMODEM. [Online, April 11, 2006.] Jupitermedia Corporation Website. http://www.webopedia.com/TERM/Z/Zmodem.html.
A file transfer protocol that was very popular during the days of analog modem transmission between bulletin boards because it handled noisy and changing line conditions very well, including satellite transmission. Funded by the Telenet packet network and developed by Chuck Forsberg in the mid-1980s, Zmodem uses a sliding window design, which is faster than the Xmodem and Ymodem protocols that came before it. The TCP protocol also uses a sliding window (see sliding window). Using variable length blocks and CRC error correction, Zmodem first sends file name, date and size before sending the data. The receiver continuously sends back the starting location of the next part of the file that is required so that crash recovery can be easily implemented by the file transfer program if the transmission fails in the middle. Many popular communications programs offer Zmodem as a file transfer option. Industrial Zmodem As a compact and proven protocol, Zmodem is used for embedded systems. Although residing in the public domain specifically for Unix systems, the heart of the protocol is available as Industrial Zmodem, a commercial product from Forsberg's company. For more information, visit www.omen.com.