IBM 3270
The IBM 3270 is 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 datastreamsIn a datastream, 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 (colour, 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. Modern users however, sometimes find this system extremely bizarre, since it is very different then any user interface encountered in the consumer market.
The 3270 has twelve, and later twenty-four, special Programmed Function Keyss, or PF keys. When one of these keys is pressed, it will 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 can 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, released in October 1983, included 3270 terminal emulation. The software program TN3270 is a modified version of Telnet which acts as a 3270 terminal emulator and can be used to connect to an IBM mainframe over a network.
Based on material from FOLDOC, used with permission.