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ibm 3270
(foldoc) | IBM 3270
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)
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