Data Dictionary - X-Z



  • Xmodem
  • Ymodem
  • Zap
  • Zmodem


A version of the UNIX system that was originally adapted by Microsoft for Intel-based personal computers. Although it has been sold by many vendors, including Microsoft, Intel, and the Santa Cruz Operation (SCO), it has become principally identified with SCO.

A file-transfer protocol used in asynchronous communications. Developed in 1977 by Ward Christensen, Xmodem is widely available as public-domain software and in numerous communications programs. Xmodem transfers information in blocks of 128 bytes. It assigns each transmitted frame a sequential block number, which is used to report errors or duplications in transmission. A 1-byte checksum (sum of the databytes) is included in each block to check for errors in transmitted data.


A variation OF THE Xmodem file-transfer protocol that includes the following enhancements: the ability to transfer information in 1-kilobyte (1024-byte) blocks; the ability to send multiple files (bath-file transmission); cyclical redundancy checking; and the ability to abort transfer by transmitting two CAN (cancel) characters in a row.


To erase permanently – for example, to zap a file, removing it without hope of retrieval; also, to damage a device, usually by discharging static electricity through it.

An enhancement of the Xmodem file-transfer protocol that handles larger data transfers with less error. Zmodem includes a feature called checkpoint restart, which resume transmission at the point of interruption, rather than at the beginning, if the communications link is broken during data transfer.

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