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Computing (FOLDOC) dictionary
IBM 3270
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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, characterset, 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
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