IBM 3270 definition 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
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.
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