The Alternate Terminal Driver Architecture
------------------------------------------------------------------------------

     In CA-Clipper, communication with I/O devices is controlled by a
     multilayered terminal system.  At the lowest level is the terminal
     driver which controls screen and keyboard activity.  It consists of a
     screen and keyboard driver that communicates directly with the I/O
     device (operating system or hardware).  It is the device specific part
     of the CA-Clipper  terminal system.

     There is, then, a higher level system that communicates with terminal
     drivers.  This system is known as the General Terminal (GT) system and
     provides general services that create CA-Clipper screen and keyboard
     commands and functions.  The following figure demonstrates:

                   +-----------------------------------------+
                   | CA-Clipper screen and keyboard commands |
                   |              and functions              |
                   |-----------------------------------------|
                   |        General Terminal (GT.OBJ)        |
                   ------------------------------------------|
                   |             Terminal Driver             |
                   |-----------------------------------------|
                   |          Screen   |   Keyboard          |
                   +-----------------------------------------+

     The default terminal driver, designed for IBM PC and 100% compatibles,
     is supplied as a library file (TERMINAL.LIB) installed into your
     \CLIPPER5\LIB directory.  This driver links into each program
     automatically if you specify no alternative terminal driver provided
     that you do not use the /R option when you compile.  An alternate
     terminal driver is supplied as a separate library (.LIB) file that links
     into an application program in place of the default terminal driver if
     you specify it on the link line.

     All alternate terminal drivers work through the General Terminal layer
     as supplied in the file GT.OBJ.  The CA-Clipper installation program
     installs this file in the \CLIPPER5\OBJ subdirectory on the drive that
     you specify, so you need not install the driver manually.