[1] : The Free On-line Dictionary of Computing (27 SEP 03)

ibm 3270
     
         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
     
     
see also:
terminals ibm mainframes i/o interrupts character set 
interrupt application program ibm pc terminal emulation tn3270 
telnet terminal emulator broken arrow 

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