YMODEM
YMODEM is the improved successor to XMODEM, supporting 1024-byte blocks, 16-bit CRC, and file name/size transfer; Chuck Forsberg extended it from XMODEM.
Purpose
It improves transfer efficiency and reliability while keeping XMODEM compatibility, and also conveys file metadata.
Mechanism
The first block carries the file name and size (NUL-terminated); subsequent blocks use 128 or 1024 bytes with a CRC16 appended, and the receiver verifies and acknowledges each block.
Use cases
- Embedded firmware upgrades
- Batch file transfer on BBSs
- Serial data backup