There are some articles about the IO subsystem of Tcl at SourceForge [http://sourceforge.net/docman/?group_id=10894]. Unfortunately one of the articles encounters a size limit imposed by SF. The text version of this article is now here on the Wiki: * [Tcl IO Drivers] aka ''The Tcl I/O system as seen by a driver (channel type)'' * ''The interaction between the I/O subsystem and the [notifier]'' [http://tcl.sourceforge.net/c-api/notifier.html] * [The interaction between the I/O subsystem and the notifier] The second article is not truncated. It might still make sense to put it here nevertheless, to have everything together. For examples see [Channel Implementations]. <> Channel