HS/Link is a file transfer protocol developed by Samuel H. Smith in 1991–1992. HS/Link is a high speed, full streaming, bidirectional, batch file transfer protocol with advanced Full-Streaming-Error-Correction. Each side of the link is allowed to provide a list of files to be sent. Files will be sent in both directions until both sides of the link are satisfied.
HS/Link is a very fast protocol for normal downloading and uploading, incorporating some new ideas (such as Full-Streaming-Error-Correction and Dynamic-Code-Substitution) to improve speed and provide greater reliability. HS/Link operates at or very near peak efficiency, often reaching 98% or more with pre-compressed files and non-buffered modems. Higher speeds are possible with buffered or error correcting modems. A number of features, such as 32 bit CRC protection, Full-Streaming-Error-Recovery and Dynamic-Code-Substitution are used for performance and security.
HS/Link can resume an aborted transfer, verifying all existing data blocks to ensure the resumed file completely matches the file being transmitted. The function can also update a file that has a small number of changed, added, or deleted blocks. An additional feature allowed remote and local users to chat depending on the file transfer bandwidth(s).