IBM 5250
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Image:IBM logo.svg IBM 5250, originally, was a particular model of a terminal device sold with the IBM S/34 minicomputer system. Similar to the IBM 3270, it is a block-oriented terminal protocol, yet is incompatible with the 3270 standard. The relationship between the terminal & system was rich: the system sent a data stream containing markup bytes indicating the boundaries of data entry fields, highlighted or colored areas, and indication that the system was busy responding to the last request from the terminal. The term "5250" now refers to the content of the data stream itself: few actual 5250 terminals still exist, although they are still used to provide a "connection of last resort", hard-wired to the host computer. They weigh about 80 lb (36 kg) and have robust construction.
The 5250 data stream definition has been refined over time to include GUI elements like pop-up windowing, check and option boxes, mouse handling, and pull-down menus. Today it is more common to use PC or web based terminal emulation packages that can interpret and display 5250 data streams. Two that are available are IBM's own iSeries Access and TN5250, an open source project, though there are many more available for free or as purchased software.
A number of these packages include additional features beyond 5250 emulation for example IBM's iSeries Access includes support for graphical system administration, remote system console connectivity, file transfers, macros, printer emulation, support for client server database connectivity and more.
Though terminal emulation is still commonly used and will be for years, because of reliability and speed issues, many applications for iSeries are being transitioned or have already switched over to use client or web based graphical interfaces.