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Ymodem: This is a protocol for transferring files during direct dial-up communications. So named because it builds on the earlier Xmodem protocol, Ymodem sends data in 1,024-byte blocks and is consequently faster than Xmodem. However, it doesn't work well on noisy phone lines, unlike its successor, Zmodem. Ymodem has undergone a few enhancements: Ymodem-Batch can send several files in one session; Ymodem-G drops software error correction, which speeds up the process by leaving hardware-based error correction in modems.