The B protocol, or CIS B, is a file transfer protocol developed for the CompuServe Information Service, and implemented in 1981. The protocol was later expanded in the QuickB version (which was an asynchronous version of the standard protocol) and later the enhanced B Plus version. It was a fairly advanced protocol for its era, supporting efficient transfers of files, commands and other data as well, and could be used in both directions at the same time in certain modes. These advanced features were not widely used, but could be found in a small number of client-side packages.