The Free On-line Dictionary of Computing (30 December 2018):

ZMODEM

    A file transfer protocol with error checking and
   crash recovery.  Developed by Chuck Forsberg.  Its transfer
   rate is similar to YMODEM-g.  Like YMODEM-g, ZMODEM does not
   wait for positive acknowledgement after each block is sent,
   but rather sends blocks in rapid succession.  If a ZMODEM
   transfer is cancelled or interrupted for any reason, the
   transfer can be resurrected later and the previously
   transferred information need not be resent.

   FTP Oakland
   (ftp://oak.oakland.edu/pub/simtelnet/msdos/zmodem/), FTP PDX
   (ftp://ftp.cs.pdx.edu/pub/zmodem/).

   Telephone: +1 900 737 7836.

   (1996-07-02)