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

CPU.