In the earlier versions of the M standard, device behavior was defined as a framework, with the details left to the implementations. GT.M supports Terminals, Sequential Disks, Magnetic Tape, Mailboxes, FIFOs, and a Null device with under this model. Subsequently device mnemonicspaces were added to the standard and some of them defined. GT.M supports the SOCKET device under this model with some extensions identified with controlmnemonics starting with the letter "Z."