XMODEMTechnology Dictionary -> XMODEM
The "Christensen" file transfer protocol, probably the most
widely available protocol used for file transfer over serial
lines (e.g. between modems). XMODEM uses 128-byte packets
with error detection, allowing the receiver to request
retransmission of a corrupted packet. XModem is fairly slow
Several variations have been proposed with increasing packet
sizes (e.g. XMODEM-1K) and different error detection (CRC
instead of checksum) to take advantage of faster modems.
Sending and receiving programs can negotiate to establish the
best protocol they both support.
Standard XMODEM specifies a one-second timeout during the
reception of characters in the data block portion of a packet.
Chuck Forsberg improved upon XMODEM by developing YMODEM and
[Chuck Forsberg, "XMODEM/YMODEM Protocol Reference"].