IBM 5250
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IBM 5250, originally, was a particular model of a terminal device sold with the IBM System/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 and 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 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.
The term "5250" now refers to the content of the data stream itself; few physical 5250 terminals still exist, although they are still used to provide a "connection of last resort," hard-wired to the host computer. Robustly constructed, 5250 terminals weighed roughly 36kg (80 lbs.) Today, it is more common to use PC or web-based terminal emulation packages that can interpret and display 5250 data streams. Two commonly-used emulators are IBM's own iSeries Access and TN5250, an open source project.
A number of modern 5250 emulaton packages include additional features beyond displaying the data stream; for example, IBM's iSeries Access includes support for graphical system administration, remote system console connectivity, file transfers, macros, printer emulation, and support for client-server database connectivity.
