Z-Modem is a widely used, duplex-capable transmission protocol with cyclic block check (CRC) for error-free data transmission.
Z-Modem is a further development of the Y-Modem, which in turn was developed from the X-Modem. Unlike its predecessors, the Z modem could dynamically adapt the length of the data blocks to the transmission conditions via automatic block length adaptation. The data packet size could range from 64 to 2,048 bytes.
The Z-Modem also offered the ability to transmit commands for communication control. In addition, with CrashRecovery it had a procedure with which the transmission was automatically continued after an interruption.