This article contains a brief description of the file transfer protocols supported by HyperTerminal.

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Kermit

Kermit is a public domain protocol developed at Columbia University. It is a sliding-window protocol that supports batch file transfers and has a maximum block size of 94 bytes. It uses either half or full duplex. Kermit is unique because it supports either 7-bit or 8-bit data transmission, enabling PC to mainframe transfers. Kermit uses either CRC or Checksum error correction. Kermit transfers the filename, date, and size.

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X-Modem

X-Modem is a public domain 8-bit, error-checking communications protocol. It is a single file protocol, has a block size of 128 bytes, and transmits using half-duplex. The filename, date, and size are not transmitted by X-Modem. You must provide the name of the file being downloaded. X-Modem uses either CRC or Checksum error checking, with CRC being the default.

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X-Modem-1K

X-Modem-1K is identical to X-Modem except that the block size is 1024 bytes.

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Y-Modem

The Y-Modem protocol is virtually the same as X-Modem, with one exception. Y-Modem uses 1024-byte blocks compared to the X-Modem 128-byte block. Because of its larger block size, Y-Modem is generally faster than X-Modem on a noise-free line. On noisy lines, X-Modem may be faster because when an error occurs, the block must be re-sent. Y-Modem must retransmit a 1024- byte block; with X-Modem's smaller blocks, less data has to be re-sent.

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Y-Modem-G

Y-Modem-G is a variant of the Y-Modem protocol. Y-Modem-G is a streaming protocol that sends 1024-byte blocks until instructed to stop. Y-Modem-G supports batch transfers. This protocol does not provide error correction or recovery. If an error is detected, the transfer is aborted. On a noise- free phone line using error-correcting modems, Y-Modem-G may be the fastest protocol.

NOTE: Y-Modem-G does not provide error correction or recovery. It is designed specifically for high-speed error-correcting modems using V.42 or other hardware error correction.

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Z-Modem

The Z-Modem file transfer protocol provides reliable file transfers with complete end-to-end data integrity. Z-Modem uses 32-bit CRC error correction and a sliding-window block up to 1024 bytes in length. Z-Modem uses intelligent error recovery, which automatically decreases block size if the phone line deteriorates and attempts to increase block size as the phone line improves. Z-Modem also provides automatic downloads. When the host computer begins transferring using Z-Modem, the remote computer recognizes this and begins receiving the download automatically.

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