Editing ZMODEM (section)

{{Short description|File transfer protocol}}
{{no footnotes|date=May 2018}}
{{Infobox networking protocol
|       title = ZMODEM
|        logo = 
|    logo alt = 
|       image = 
|   image alt = 
|     caption = 
|    is stack = 
|     purpose = file transfer protocol
|   developer = [[Chuck Forsberg]]
|        date = {{Start date and age|  1986  |  |  }}<!--Fill in: Year (4 digits), month and day (2 digits)-->
|    based on = 
|  influenced = 
|    osilayer = 
|       ports = None
|        rfcs = 
|    hardware = [[modem]]s
}}

'''ZMODEM''' is an inline [[Comparison of file transfer protocols|file transfer protocol]] developed by [[Chuck Forsberg]] in 1986, in a [[project]] funded by [[Telenet]] in order to improve file transfers on their [[X.25]] network. In addition to dramatically improved performance compared to older protocols, ZMODEM offered restartable transfers, auto-start by the sender, an expanded 32-bit [[cyclic redundancy check|CRC]], and [[Escape character|control character quoting]] supporting [[8-bit clean]] transfers, allowing it to be used on networks that would not pass control characters.

In contrast to most transfer protocols developed for [[bulletin board system]]s (BBSs), ZMODEM 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, and most remained [[backward compatible]] and would successfully complete transfers with "classic" XMODEM implementations. This list includes Forsberg's own [[YMODEM]].

ZMODEM eschewed backward compatibility in favor of producing a radically improved protocol. It performed at least as well as any of the high-performance varieties of XMODEM, did so over links that previously did not work at all, like X.25, or had poor performance, like [[Telebit]] modems, and included useful features found in few other protocols. ZMODEM became extremely popular on [[bulletin board system]]s (BBS) in the early 1990s, becoming a standard as widespread as XMODEM had been before it.