YMODEM
A file transfer
protocol used between
modems.
YMODEM was developed by Chuck Forsberg as the successor to
XMODEM and was itself succeeded by
ZMODEM.
XMODEM used 128-byte
packets, 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"].
