Difference between Xmodem, Ymodem and Zmodem

These three Xmodem, Ymodem and Zmodem are file transferring methods are the preferred methods. They have built-in error correction scheme and this means if there are any errors encountered while transferring a file, the computer will try to fix the error by having erroneous pieces of the file re-sent. These errors typically occur when there is some line noise, which could garble the characters, or in other instances.


Xmodem developed in 1977 by Ward Christensen and Xmodem is one of the most popular file-transfer protocols. Although Xmodem 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.

Xmodem can be implemented either in software or in hardware. Many modems, and almost all communications software packages, support Xmodem. However, it is useful only at relatively slow data transmission speeds (less than 4,800 bps).

Enhanced versions of Xmodem that work at higher transmission speeds are known as Ymodem and Zmodem.


Ymodem was designed by Chuck Forsberg. Xmodem is an asynchronous communications protocol that extends Xmodem by increasing the transfer block size and by supporting batch file transfers. This enables you to specify a list of files and send them all at one time. With Xmodem, you can send only one file at a time.


Zmodem also an asynchronous communications protocol and it greatly simplifies file transfers compared to xmodem. In addition to a friendly user interface, zmodem provides Personal Computer and other users an efficient, accurate, and robust file transfer method. It provides faster data transfer rates and better error detection than Xmodem. In particular, Zmodem supports larger block sizes and enables the transfer to resume where it left off following a communications failure.

Zmodem provides complete end-to-end data integrity between application programs. Its 32 bit CRC catches errors that sneak into even the most advanced networks. Advanced file management features include AutoDownload (Automatic file Download initiated without user intervention), Display of individual and total file lengths and transmission time estimates, Crash Recovery, selective file transfers, and preservation of exact file date and length.

Difference between Xmodem and Ymodem

Both are similar type of protocols but X-modem does not support batch file transfers, but is more likely to be found on more terminal programs. To download a file, first type “sx filename” (by default, X modem uses binary transfers), and then use the “receive Xmodem” command on your terminal program to receive the file. To perform an upload to Wiliki, type “rx”, followed by the file name to transfer the file.

The main difference between Xmodem and Ymodem is Ymodem’s ability to send several files at once. Because Zmodem has a recovery feature that Ymodem lacks

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  1. Martin says:

    Thanks for sharing all file transfer protocols Xmodem, Ymodem and Zmodem.

  2. Puneeth says:

    Nice to read the difference between all the file transfer protocols and it is very use any Network engineers.

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