The 3270 Information Display System, a product from IBM, was, prior to the arrival of the PC, the way that almost the entire corporate world interfaced with a computer. When first produced (the early 1970s), a 3270 display terminal was considered a vast improvement over its predecessor, the 2260.
The 3277 terminal was a non-graphical (text only) monochrome (black screen with green letters) display that buffer ed data so that key strokes could be saved until the ENTER key was pressed. (Previous terminals sent every key stroke immediately to the computer to which the terminal was attached.) The 3277 was also field-oriented rather than line-oriented which meant that a program could write an output data stream to the terminal based on application-oriented fields rather than having to create the display output line by line. A number of 3277s could be attached to a control unit or cluster controller which in turn was attached to an IBM mainframe computer. Terminals could be attached to the computer on a relatively high-bandwidth local link called a channel or remotely over a telecommunication link that was either dedicated (usually a leased line ) or dial-up .
After the personal computer arrived with its own self-sufficient operating system and applications, it gradually replaced the 3270 system in much of the corporate world (although there almost certainly are some working 3270s in use as this is being written). A 3270 terminal became the most prominent example of what became known as a " dumb terminal ," since it relied entirely on its attachment to a mainframe (and sometimes a minicomputer ) for its "brains." The PC attached to a mainframe then became known generically as an " intelligent workstation ." It could run its own programs independently of the mainframe and it could also interface with mainframe applications. There was one product attempt to blend the two, called the 3270 PC.
The terminals themselves were the 3277 (which attached to a control unit), a 3275 standalone terminal (for locations where only a single terminal was needed), the 3278 (a sleeker version of the 3277), and the 3279 color terminal. The control units were the 3271 (channel attachment), 3272 (telecommunication attachment), and the 3274 (a control unit with a smaller form factor that could handle up to 32 terminals). For about 15 years, the 3270 family, one of IBM's most successful products ever, was a ubiquitous feature of offices the world over. The PC changed all that.
However, many thousands of corporate legacy application programs written to interact with users at 3270s are being used from PCs equipped with software known generally as 3270 emulator s. TN3270 is a program that provides PC users remote ( Telnet ) connection to an IBM computer that is running 3270 applications.