A file transfer protocol
used between modem
YMODEM was developed by Chuck Forsberg as the successor to XMODEM
and was itself succeeded by ZMODEM
XMODEM used 128-byte packet
s, YMODEM can also use 1 kilobyte packets.
Whereas YMODEM is a batch protocol, YMODEM-G
is a non-stop version.
File sizes are included in the YMODEM header when sending both binary and text files.
Thus files transferred via YMODEM should preserve their exact length.
File modification times may also be present in the YMODEM header.
YModem can fall back
to smaller packets when necessary but there is no backward compatibility with XModem's error detection.
[Chuck Forsberg, "XMODEM/YMODEM Protocol Reference"].