IBM 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)

The IBM 3270 is a family of block oriented display and printer computer terminals introduced by IBM in 1971