3270

IBM 3270
3270

   <hardware> A class of {terminals} made by {IBM} known as
   "Display Devices", normally used to talk to {IBM}
   {mainframes}.  The 3270 attempts to minimise the number of
   {I/O} {interrupts} required by accepting large blocks of data,
   known as datastreams, in which both text and control (or
   formatting functions) are interspersed allowing an entire
   screen to be "painted" as a single output operation.  The
   concept of "formatting" in these devices allows the screen to
   be divided into clusters of contiguous character cells for
   which numerous attributes (color, highlighting, {character
   set}, protection from modification) can be set.  Further,
   using a technique known as 'Read Modified' the changes from
   any number of formatted fields that have been modified can be
   read as a single input without transferring any other data,
   another technique to enhance the terminal throughput of the
   CPU.

   The 3270 had twelve, and later twenty-four, special Programmed
   Function Keys, or PF keys.  When one of these keys was
   pressed, it would cause the device to generate an I/O
   {interrupt} and present a special code identifying which key
   was pressed.  {Application program} functions such as
   termination, page-up, page-down or help could be invoked by a
   single key-push, thereby reducing the load on very busy
   processors.

   A version of the {IBM PC} called the "3270 PC" was released in
   October 1983.  It included 3270 {terminal emulation}.

   {tn3270} is modified version of {Telnet} which acts as a 3270
   {terminal emulator} and can be used to connect to an IBM
   computer over a network.

   See also {broken arrow}.

   (1995-02-07)