Xmodem is one of the most popular file-transfer protocols. It is a relatively simple protocol, it is fairly effective at detecting errors. It works by sending blocks of data together with a checksum and then waiting for acknowledgment of the block's receipt. The waiting slows down the rate of data transmission considerably, but it ensures accurate transmission. Enhanced versions of Xmodem that work at higher transmission speeds are known as Ymodem and Zmodem.
Meaning of XMODEM in English
DAX English glossary of key connectivity terms. Английский глоссарий основных терминов по коммуникациям DAX. 2012