The IBM 5250 terminal
The IBM 5250 Display stations are a long lived, popular family of terminals originally produced by IBM as a component of their System/3 computer in 1969. Designed specifically for small businesses the midrange System/3 offered a cheaper alternative to the larger, more expensive systems colloquially referred to as ‘Big Iron‘ , which were priced out of the reach or smaller organizations.
The IBM 5250 terminal was similar to its cousin the IBM 3270 Information Display System (or 3270 terminal). It connected to the host system using the proprietary IBM SNA protocol via a Twinax cable (coax type cable). It implemented block mode communication like the 3270, however the two terminals where not compatible. While the IBM 5250 had its own version of block mode and the SNA protocol, from the users prospective the 5250 Display Stations presented the display just like the mainframe screens of the 3270 terminal. Data was still clearly presented in ‘fields’ that the user could easily navigate and input date. The terminal response was quick thanks to all inputted data being buffered locally and then transmitted when the user hit enter. The 5250 gave the user more information about the terminal status, for example a busy indicator would let the user know that the terminal is still waiting for the host to respond. The 5250 came with a color screen and also had a mechanical feedback keyboard that made a clicking sound as you pressed each key in order to simulate the feel of the typewriters of the day. (Side note: Funnily enough the ‘clicky’ PC equivalent of this type of keyboard, the model M, remains highly sought after although it obviously doesn’t support USB. Here’s a nice modern equivalent which does.)
The 5250 was able to connect to a succession of midrange systems starting with the System/3, and continuing with it’s descendants the System/32, System/34, System/36, System/38, AS400 and the iSeries.
By the time IBM released the AS/400 in 1988, IBM had sold over 250,000 of their System/3x series systems since the release of the System/34 in 1977, making it the most widely used range of midrange systems. The AS/400 series later morphed into the iSeries and the System i, with most users of the older hosts upgrading to the newer and faster offerings. This in turn increased the popularity of the 5250 terminals.
It took some time before PC based terminal emulation really started to encroach on the territory of the physical 5250 terminals range. Historically, as was the case with many other systems, terminals began to disappear as the cost of PC’s dropped and they become ubiquitous in the business environment. Operators began to rationalize their host connectivity solutions and do away with having more than one systems taking up desktop real estate.
However because IBM’s midrange systems communicated via the SNA protocol, ‘gateway’ solutions were deployed on PC networks to facilitate connections between PC’s running terminal emulation software, typically on a TCP/IP network and the SNA host. These offered an alternative to physical terminals or the use of hardware emulation cards in every PC connecting to the host. The SNA gateway that was connecting to the host acted both to manage the client connection and as a protocol converter between the SNA host and the TCP/IP client, allowing the PC running 5250 terminal emulation software to communication with the host system.
There where several different flavors of SNA Gateways released by different companies, such as IBM, SCO and Microsoft to name but a few. Microsoft’s SNA Gateway was widely used because it allowed the user to choose the Emulation vendor that best suited their requirements. For example you could use the emulation that came with the MS SNA gateway or a 3rd party MS SNA compatible client like TTWin.
Eventually IBM introduced the TN5250 protocol, the 5250’s version of Telnet, operating over TCP/IP. This really was the nail in the coffin for the physical 5250 terminal and opened up the emulation market, eliminating the need for special PC cards or SNA Gateways and giving rise to a new generation of cheaper terminal emulation software packages.
It should be noted that TN5250 differs from TN3270 and both of these differ from the standard telnet protocol used by most other emulated terminals.
Nowadays System/3x series systems have been retied or upgraded to an AS400 or, more likely, one of the later iSeries systems. Of those systems running a legacy application that requires the 5250 terminal, most would be using a terminal emulation connected via the TN5250 protocol. Some applications have also had a web frontend written for them so that emulation isn’t required at all, while others still have used terminal emulators with API’s or OCX controls to write a web or GUI frontend for an application that requires the 5250 terminal. This option is usually taken because it is cheaper to write an application using a emulators OCX then it is to make changes to the host application.