Microsoft KB Archive/114451

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Windows Terminal Supports XModem-1K Protocol

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Q114451

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The information in this article applies to:


 * Microsoft Windows versions 3.1, 3.11
 * Microsoft Windows for Workgroups versions 3.1, 3.11
 * Microsoft Windows NT Server version 3.1
 * Microsoft Windows NT Workstation version 3.1

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SUMMARY
The Windows Terminal program (TERMINAL.EXE) included with Microsoft Windows, Windows for Workgroups, and Windows NT supports the XModem-1K binary file transfer protocol for faster and more efficient file transfers.

MORE INFORMATION
Windows Terminal supports the Kermit and XModem/cyclic redundancy check (CRC) error-correcting file-transfer protocols. These protocols are used to transfer binary files, such as executable programs (.COM and .EXE files) and other files including ASCII text. These protocols have the ability to detect and correct errors.

Files transferred with the XModem/CRC protocol are divided into packets (sometimes referred to as blocks) and then a mathematical computation is performed to create a signature number. This signature number is sent with the packet to be checked on the receiving end. If the numbers do not match, an error is detected and the packet is retransmitted.

The XModem/CRC protocol supplied with Terminal defaults to a 128-byte packet (block) size. The signature number is added to each 128 bytes transferred. Because of the small size of the packets, the signature number increases the overall amount of data transferred significantly.

The XModem-1K protocol increases the packet size to 1024 bytes (1 kilobyte). This allows for faster transfers than 128-byte packets because the signature number is only added for every 1024 bytes transferred.

Using XModem-1K is eight times more efficient than the default (XModem/CRC) with 128-byte packets.

Many bulletin board systems (BBSs), support XModem-1K. Additionally, many commercial dial-up services, support the XModem-1K protocol.

To enable XModem-1K in Terminal, select Binary Transfers from the Settings menu and choose XModem/CRC. Then choose XModem-1K, if available, when downloading. Terminal automatically adjusts to the 1K-packet size when you select XModem-1K on the BBS or service from which you are downloading.