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66-477: ISPF primarily provides an IBM 3270 terminal interface with a set of panels . Each panel may include menus and dialogs to run tools on the underlying environment, e.g., Time Sharing Option (TSO). Generally, these panels just provide a convenient interface to do tasks—most of them execute modules of IBM mainframe utility programs to do the actual work. ISPF is frequently used to manipulate z/OS data sets via its Program Development Facility (ISPF/PDF). ISPF

132-569: A context menu . F2 is used in many Windows applications such as Windows Explorer, Excel, Visual Studio and other programs to access file or field edit functions, such as renaming a file. F4 is used in some applications to make the window "fullscreen", like in 3D Pinball: Space Cadet . In Microsoft IE, it is used to view the URL list of previously viewed websites. Other function key assignments common to all Microsoft Office applications are: F7 to check spelling, Alt + F8 to call

198-472: A control unit (the 3275 and 3276 included an integrated control unit). Originally devices were connected to the control unit over coaxial cable; later Token Ring , twisted pair , or Ethernet connections were available. A local control unit attaches directly to the channel of a nearby mainframe. A remote control unit is connected to a communications line by a modem . Remote 3270 controllers are frequently multi-dropped , with multiple control units on

264-606: A 1.44 MB 3.5" floppy drive and IND$ FILE transfer. Several third-party manufacturers produced 3270 displays besides IBM. GTE manufactured the IS/7800 Video Display System, nominally compatible with IBM 3277 displays attached to a 3271 or 3272. An incompatibility with the RA buffer order broke the logon screen in VM/SE (SEPP). Harris manufactured the 8000 Series Terminal Systems, compatible with IBM 3277 displays attached to

330-421: A 17", amber monochrome plasma display unit announced March 8, 1983, capable of displaying in various modes, including four independent 3278 model 2 terminals, or a single 160×62 terminal; it also supports partitioning. The 3290 supports graphics through the use of programmed symbols . A 3290 application can divide its screen area up into as many as 16 separate explicit partitions (logical screens). The 3290

396-464: A 3271 or 3272. Harris later manufactured the 9100–9200 Information Processing Systems, which included Informer Computer Terminals manufactured a special version of their model 270 terminal that was compatible with IBM 3270 and its associated coax port to connect to a 3x74. Documentation for the following is available at AT&T introduced the Dataspeed 40 terminal/controller, compatible with

462-446: A 3×4 matrix at the right of the keyboard. Later models replaced this with a numeric keypad , and moved the function keys to 24 keys at the top of the keyboard. The original IBM PC keyboard ( PC/XT , 1981) had 10 function keys (F1–F10) in a 2×5 matrix at the left of the keyboard; this was replaced by 12 keys in 3 blocks of 4 at the top of the keyboard in the Model M ("Enhanced", 1984). In

528-465: A 78 key version with twelve. Both versions had two Program Attention (PA) keys. The data entry keyboard had five PF keys and two PA keys. The operator console keyboard had twelve PF keys and two PA keys. Later 3270s had an Attention key, a Cursor Select key, a System Request key, twenty-four PF keys and three PA keys. There was also a TEST REQ key. When one of these keys is pressed, it will cause its control unit to generate an I/O interrupt to

594-475: A consequence, the labels on Macintosh keyboards have changed over time to reflect the newer mappings of later Mac OS X versions: for instance, on a 2006 MacBook Pro, functions keys F3 , F4 and F5 are labelled for volume down/volume up, whereas on later MacBook Pros (starting with the 2007 model), the volume controls are located on function keys F10 to F12 where they are mapped to various functions . Any recent version of Mac OS X or macOS

660-512: A full-screen text editor, a menu system, and a PANEL facility to create 3270 full-screen applications. The modified data tag is well suited to converting formatted, structured punched card input onto the 3270 display device. With the appropriate programming, any batch program that uses formatted, structured card input can be layered onto a 3270 terminal. IBM's OfficeVision office productivity software enjoyed great success with 3270 interaction because of its design understanding. And for many years

726-404: A help window. F3 is commonly used to activate a search function in applications, often cycling through results on successive presses of the key. ⇧ Shift + F3 is often used to search backwards. Some applications such as Visual Studio support Control + F3 as a means of searching for the currently highlighted text elsewhere in a document. F5 is also commonly used as

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792-408: A large number of mainframe & PC programs. ISPF remembers each user's choices for such things as screen colors & layout, the location of the command line and scrolling preferences. It also remembers the last-used data set names on each panel, so the next time the panel is used the names are already filled in. This is very convenient for mainframe programmers because they frequently work with

858-440: A line. IBM 3270 devices are connected to a 3299 multiplexer or to the cluster controller, e.g., 3271, 3272, 3274, 3174, using RG-62, 93 ohm, coax cables in a point to point configuration with one dedicated cable per terminal. Data is sent with a bit rate of 2.3587 Mbit/s using a slightly modified differential Manchester encoding . Cable runs of up to 1,500 m (4,900 ft) are supported, although IBM documents routinely stated

924-411: A new version and a compatible product for CMS under Virtual Machine Facility/370 Release 5. In 1980 IBM changed its name to System Productivity Facility and offered a version for CMS under VM/SP . In 1982 IBM changed the name to Interactive System Productivity Facility, split off some facilities into Interactive System Productivity Facility/Program Development Facility (ISPF/PDF) and offered

990-512: A program to allow use of mainframe ISPF applications and edit macros written in REXX on DOS, OS/2 and Windows; the last release was 1.2.8 in 1994. Freeware ISPF-style editors for Windows include SPF/SE and SPFlite . In 1994 IBM introduced a built-in downloadable client program called the ISPF Workstation Agent (WSA) that can install and run on OS/2, Windows and selected UNIX workstations;

1056-455: A reload key in many web browsers and other applications, while F11 activates the full screen/ kiosk mode on most browsers. Under the Windows environment, Alt + F4 is commonly used to quit an application; Ctrl + F4 will often close a portion of the application, such as a document or tab. F10 generally activates the menu bar , while ⇧ Shift + F10 activates

1122-511: A secondary size of 32x80, 4 and 4+ have a secondary size of 43x80 and 5 and 5+ have a secondary size of 27x132. An application can override the primary and alternate screen sizes for the extended mode. The 3180 also supported a single explicit partition that could be reconfigured under application control. The IBM 3191 Display Station is an economical monochrome CRT. Models A and B are 1920 characters 12-inch CRTs. Models D, E and L are 1920 or 2560 character 14-inch CRTs. The IBM 3193 Display Station

1188-484: A single output operation. The concept of formatting in these devices allows the screen to be divided into fields (clusters of contiguous character cells) for which numerous field attributes, e.g., color, highlighting, character set, protection from modification, can be set. A field attribute occupies a physical location on the screen that also determines the beginning and end of a field. There are also character attributes associated with individual screen locations. Using

1254-473: A technique known as read modified, a single transmission back to the mainframe can contain the changes from any number of formatted fields that have been modified, but without sending any unmodified fields or static data. This technique enhances the terminal throughput of the CPU , and minimizes the data transmitted. Some users familiar with character interrupt-driven terminal interfaces find this technique unusual. There

1320-599: A version for VSE/AF . In 1984 IBM released ISPF Version 2 and ISPF/PDF Version 2; the VM versions allowed the user to select either the PDF editor or XEDIT . IBM eventually merged PDF back into the base product. ISPF can also be run from a z/OS batch job. When a foreground (interactive) TSO user invokes ISPF, it provides a menuing system, normally with an initial display of a Primary Option Menu this provides them access to many useful tools for application development and for administering

1386-413: Is a Distributed Function Terminal (DFT) and requires that the controller do a downstream load (DSL) of microcode from floppy or hard disk. The 3180 was a monochrome display, introduced on March 20, 1984, that the user could configure for several different basic and extended display modes; all of the basic modes have a primary screen size of 24x80. Modes 2 and 2+ have a secondary size of 24x80, 3 and 3+ have

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1452-428: Is a high-resolution, portrait-type, monochrome, 380mm (15 inch) CRT image display providing up to letter or A4 size document display capabilities in addition to alphanumeric data. Compressed images can be sent to the 3193 from a scanner and decompression is performed in the 3193. Image data compression is a technique to save transmission time and reduce storage requirements. The IBM 3194 is a Display Station that features

1518-469: Is able to detect which generation of Apple keyboard is being used, and to assign proper default actions corresponding to the labels shown on this Apple keyboard (provided that this keyboard was manufactured before the release of the version of Mac OS X being used). As a result, default mappings are sometimes wrong (i.e., not matching the labels shown on the keyboard) when using a recent USB Apple keyboard on an older version of Mac OS X, which doesn't know about

1584-429: Is also a read buffer capability that transfers the entire content of the 3270- screen buffer including field attributes. This is mainly used for debugging purposes to preserve the application program screen contents while replacing it, temporarily, with debugging information. Early 3270s offered three types of keyboards. The typewriter keyboard came in both a 66 key version, with no programmed function (PF) keys , and

1650-502: Is user-extensible and it is often used as an application programming interface . Many vendors have created products for z/OS that use the ISPF interface. An early version was called Structured Programming Facility ( SPF ) and introduced in SVS and MVS systems in 1974. IBM chose the name because SPF was introduced about the same time as structured programming concepts. In 1979 IBM introduced

1716-733: The PROFS calendar was the most commonly displayed screen on office terminals around the world. A version of the WordPerfect word processor ported to System/370 was designed for the 3270 architecture. 3270 devices can be a part of an SNA – System Network Architecture network or non-SNA network. If the controllers are SNA connected, they appear to SNA as PU – Physical Unit type 2.0 (PU2.1 for APPN) nodes typically with LU – Logical Unit type 1, 2, and 3 devices connected. Local, channel attached, controllers are controlled by VTAM – Virtual Telecommunications Access Method . Remote controllers are controlled by

1782-631: The URL in the address bar. Function Keys are also heavily used in the BIOS interface. Generally during the power-on self-test , BIOS access can be gained by hitting either a function key or the Del key. In the BIOS keys can have different purposes depending on the BIOS. However, F10 is the de facto standard for save and exit which saves all changes and restarts the system. During Windows 10 startup, ⇧ Shift + F8

1848-478: The classic Mac OS , the function keys could be configured by the user, with the Function Keys control panel, to start a program or run an AppleScript . macOS assigns default functionality to (almost) all the function keys from F1 to F12 , but the actions assigned by default to these function keys have changed a couple of times over the history of Mac products and corresponding Mac OS X versions . As

1914-680: The z/OS operating system. Such tools include Underlying ISPF/PDF is an extensive set of tools that allow application developers to create panel-driven applications, and a set of guidelines to promote consistent use of ISPF functions. A "panel" is a character-based "window" which can encompass all or part of a 3270 session's screen real estate. See Text-based user interfaces . Most mainframe software vendors used ISPF functions to create their applications, so their tools are similar in appearance and operation to ISPF. Similarly, many installations write their own informal tools that use ISPF services. ISPF services are generally available to any programmer in

1980-481: The 'editor interface' which lets an application program display arbitrary data in the familiar editor panel. Thus many vendor packages use this familiar interface. ISPF is designed to be customized for each user (a fairly new concept in 1974, when it was introduced). Some of the customization is global and some is specific to an ISPF application. It supports a set of 24 function keys which, when pressed, execute commands. These are customizable: Each user can replace

2046-485: The 3174 controller also enabled multiple sessions from a CUT type terminal. The 3278, along with the 3279 color display and the 3287 printer, introduced the Extended Display Stream (EDS) as the framework for new features. The IBM 3279 was IBM's first color terminal. IBM initially announced four models, and later added a fifth model for use as a processor console. The 3279 was introduced in 1979. The 3279

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2112-505: The 3270 data stream is forwarded to the display by the controller. The display interprets the 3270 protocol itself. In addition to passing the 3270 data stream directly to the terminal, allowing for features like EAB — Extended Attributes, Graphics, etc., DFT also enabled multi sessions (up to 5 simultaneous), featured in the 3290 and 3194 multisession displays. This feature was also widely used in 2nd generation 3270 terminal emulation software. The MLT — Multiple Logical Terminals feature of

2178-463: The 3270 data stream terminates. For CUT (Control Unit Terminal) displays, the stream terminates in the display controller, the controller instructs the display to move the cursor, position a character, etc. EBCDIC is translated by the controller into '3270 Character Set', and keyboard scan-codes from the terminal, read by the controller through a poll, is translated by the controller into EBCDIC. For DFT (Distributed Function Terminal) type displays, most of

2244-474: The 3275 and 3277 are the selector-pen , ASCII rather than EBCDIC character set, an audible alarm, and a keylock for the keyboard. A keyboard numeric lock was available and will lock the keyboard if the operator attempts to enter non-numeric data into a field defined as numeric. Later an Operator Identification Card Reader was added which could read information encoded on a magnetic stripe card . Generally, 3277 models allow only upper-case input, except for

2310-403: The 3rd party system was compatible with the 3270 data stream terminated in the unit, but not as 'Plug compatibility' equipment, also were compatible at the coax level thereby allowing IBM terminals to be connected to a 3rd party controller or vice versa. Modern applications are sometimes built upon legacy 3270 applications, using software utilities to capture ( screen scraping ) screens and transfer

2376-457: The IBM 3270 protocol is still commonly used via TN3270 clients, 3270 terminal emulation or web interfaces to access mainframe-based applications, which are sometimes referred to as green screen applications . The 3270 series was designed to connect with mainframe computers, often at a remote location, using the technology then available in the early 1970s. The main goal of the system was to maximize

2442-511: The IBM 3275, in 1980. IBM had two different implementations for supporting graphics. The first was implemented in the optional Programmed Symbol Sets (PSS) of the 3278, 3279 and 3287, which became a standard feature on the later 3279-S3G, a.k.a. 3279G, and was based on piecing together graphics with on-the-fly custom-defined symbols downloaded to the terminal. The second later implementation provided All Points Addressable (APA) graphics, a.k.a. Vector Graphics, allowing more efficient graphics than

2508-646: The NCP – Network Control Program in the Front End Processor i.e. 3705 , 3720 , 3725 , 3745 , and VTAM. One of the first groups to write and provide operating system support for the 3270 and its early predecessors was the University of Michigan, who created the Michigan Terminal System in order for the hardware to be useful outside of the manufacturer. MTS was the default OS at Michigan for many years, and

2574-641: The data to web pages or GUI interfaces. In the early 1990s a popular solution to link PCs with the mainframes was the Irma board , an expansion card that plugged into a PC and connected to the controller through a coaxial cable. 3270 simulators for IRMA and similar adapters typically provide file transfers between the PC and the mainframe using the same protocol as the IBM 3270 PC . The IBM 3270 display terminal subsystem consists of displays, printers and controllers. Optional features for

2640-458: The default commands assigned to any key with his own preferred command (or series of commands). User settings are stored centrally, so that the user can logon from any terminal and that session will remember their previously-chosen commands for each key. Most personal computers copied this, and have a set of 12 or 24 function keys. Even some defaults have endured: the F1 key triggers a "help" function on

2706-529: The host computer and present an Attention ID (AID) identifying which key was pressed. Application program functions such as termination, page-up, page-down, or help can be invoked by a single key press, thereby reducing the load on very busy processors. A downside to this approach was that vi -like behavior, responding to individual keystrokes, was not possible. For the same reason, a port of Lotus 1-2-3 to mainframes with 3279 screens did not meet with success because its programmers were not able to properly adapt

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2772-446: The line number fields with a one or two character code representing the command to be applied at that line followed by an optional number which further modifies the supplied command. The editor has several key features: The editor can also be invoked in a 'view' mode. It behaves like the editor, but does not allow saving the data. Edited files can also be saved under a different name, creating or replacing another file. ISPF provides

2838-746: The macros dialog, Alt + F11 to call the Visual Basic Editor and ⇧ Shift + Alt + F11 to call the Script Editor. In Microsoft Word, ⇧ Shift + F1 reveals formatting. In Microsoft PowerPoint, F5 starts the slide show, and F6 moves to the next pane. ⇧ Shift + F9 exits the MS-DOS Shell if it is running. WordPerfect for DOS is an example of a program that made heavy use of function keys. In Internet Explorer 6 and Internet Explorer 7 , F12 opens Internet Explorer Developer Toolbar . F6 highlights

2904-548: The mainframe. The editor screen is formatted with 2 lines (info & command line) at the top (or bottom – user choice), a six character line number column in the left margin, and the remainder of the screen width being filled with the records of the dataset being edited. Primary commands (which apply to the whole dataset) such as Find, Print, Sort, etc. are typed in the command line. Line commands (which apply only to specific line(s)) such as copy, move, repeat, insert, exclude, delete, text flow, text split are entered by over-typing

2970-491: The maximum supported coax cable length was 2,000 ft (610 m). Originally devices were equipped with BNC connectors , which later was replaced with special so-called DPC – Dual Purpose Connectors supporting the IBM Shielded twisted pair cabling system without the need for so-called red baluns . In a data stream, both text and control (or formatting functions) are interspersed allowing an entire screen to be painted as

3036-645: The mixed EBCDIC/APL or text keyboards, which have lower case. Lower-case capability and dead keys were available as an RPQ ( Request Price Quotation ); these were added to the later 3278 & 3279 models. A version of the IBM PC called the 3270 PC , released in October 1983, includes 3270 terminal emulation . Later, the 3270 PC/G (graphics), 3270 PC/GX (extended graphics), 3270 Personal Computer AT, 3270 PC AT/G (graphics) and 3270 PC AT/GX (extended graphics) followed. There are two types of 3270 displays in respect to where

3102-481: The models 2B and 3B supported seven colors, and when equipped with the optional Programmed Symbol Set feature had a loadable character set that could be used to show graphics. The Programmed Symbol Set feature could be added in the field, and was standard in the model S3G. The IBM 3279 with its graphics software support, Graphical Data Display Manager (GDDM), was designed at IBM's Hursley Development Laboratory , near Winchester, England . The 3290 Information Panel

3168-464: The more common "F-number" designations. The Singer/Friden 2201 Flexowriter Programmatic, introduced in 1965, had a cluster of 13 function keys, labeled F1 to F13 to the right of the main keyboard. Although the Flexowriter could be used as a computer terminal , this electromechanical typewriter was primarily intended as a stand-alone word processing system. The interpretation of the function keys

3234-468: The new function key mapping of this keyboard (e.g., because Mission control and Launchpad didn't exist at that time, the corresponding labels shown on the keyboard can't match the default actions assigned by older versions of Mac OS X, which were Exposé and Dashboard). It can be noted that: Under MS-DOS , individual programs could decide what each function key meant to them, and the command line had its own actions. For example, F3 copied words from

3300-535: The number of terminals that could be used on a single mainframe. To do this, the 3270 was designed to minimize the amount of data transmitted, and minimize the frequency of interrupts to the mainframe. By ensuring the CPU is not interrupted at every keystroke, a 1970s-era IBM 3033 mainframe fitted with only 16 MB of main memory was able to support up to 17,500 3270 terminals under CICS . Most 3270 devices are clustered , with one or more displays or printers connected to

3366-435: The older technique. The first terminal to support APA / Vector graphics was the 3179G terminal that later was replaced by first the 3192G and later the 3472G. Both implementations are supported by IBM GDDM — Graphical Data Display Manager first released in 1979, and by SAS with their SAS/GRAPH software. Function keys A function key is a key on a computer or terminal keyboard that can be programmed to cause

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3432-425: The operating system or an application program to perform certain actions, a form of soft key . On some keyboards/computers, function keys may have default actions, accessible on power-on. Function keys on a terminal may either generate short fixed sequences of characters, often beginning with the escape character ( ASCII 27), or the characters they generate may be configured by sending special character sequences to

3498-852: The presence of 3270 terminals and provided a set of ISPF panels and supporting programs. Conversational Monitor System (CMS) in VM has support for the 3270 continuing to z/VM . Time Sharing Option (TSO) in OS/360 and successors has line mode command line support and also has facilities for full screen applications, e.g., ISPF . Device Independent Display Operator Console Support (DIDOCS) in Multiple Console Support (MCS) for OS/360 and successors supports 3270 devices and, in fact, MCS in current versions of MVS no longer supports line mode, 2250 and 2260 devices. The SPF and Program Development Facility (ISPF/PDF) editors for MVS and VM/SP (ISPF/PDF

3564-567: The previous command to the current command prompt. Following the IBM Common User Access guidelines, the F1 key gradually became universally associated with Help in most early Windows programs. To this day, Microsoft Office programs running in Windows list F1 as the key for Help in the Help menu. Internet Explorer in Windows does not list this keystroke in the help menu, but still responds with

3630-451: The same files repeatedly. Many of the early users of PCs were mainframe programmers or users, who were accustomed to and liked the ISPF panel system. This led several companies to create partial clones of ISPF that run on DOS , OS/2 , Windows or Unix PC systems. In 1984 IBM introduced the EZ-VU dialog manager for DOS PCs, and later OS/2 . In 1991 Tritus, Inc introduced Tritus SPF (TSPF),

3696-413: The shop, and can be used to write panels for either personal or shop-wide use, writing in either compiled languages such as HLASM , C , COBOL , PL/I , or interpreted languages such as CLIST , REXX and ooRexx . ISPF applications can be used to perform so-called "file tailoring" functions, customisation of specially crafted JCL members called "skeletons", which can then be submitted as batch jobs to

3762-420: The spreadsheet's user interface to a screen at a time rather than character at a time device. But end-user responsiveness was arguably more predictable with 3270, something users appreciated. Following its introduction the 3270 and compatibles were by far the most commonly used terminals on IBM System/370 and successor systems. IBM and third-party software that included an interactive component took for granted

3828-406: The terminal. On a standard computer keyboard, the function keys may generate a fixed, single byte code, outside the normal ASCII range, which is translated into some other configurable sequence by the keyboard device driver or interpreted directly by the application program. Function keys may have abbreviations or pictographic representations of default actions printed on/besides them, or they may have

3894-468: The top left of the keyboard, with paper labels. The HP 9830A (1972) was an early desktop computer, and one of the earliest specifically computing uses. HP continued its use of function keys in the HP 2640 (1975), which used screen-labeled function keys , placing the keys close to the screen, where labels could be displayed for their function. NEC 's PC-8001 , introduced in 1979, featured five function keys at

3960-439: The top of the keyboard, along with a numeric keypad on the right-hand side of the keyboard. Their modern use may have been popularized by IBM keyboards: first the IBM 3270 terminals, then the IBM PC . IBM use of function keys dates to the IBM 3270 line of terminals, specifically the IBM 3277 (1972) with 78-key typewriter keyboard or operator console keyboard version, which both featured 12 programmed function (PF) keys in

4026-542: The z/OS version of ISPF only includes WSA for Windows and selected UNIX workstations. WSA communicates directly with ISPF on z/OS and provides a point-and-click graphical user interface automatically. The ISPF Workstation Agent can be used to edit PC based files from the ISPF editor to take advantage of the editor's strengths. IBM 3270 The IBM 3270 is a family of block oriented display and printer computer terminals introduced by IBM in 1971 and normally used to communicate with IBM mainframes . The 3270

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4092-551: Was available for VM, but little used) and the XEDIT editors for VM/SP through z/VM make extensive use of 3270 features. Customer Information Control System (CICS) has support for 3270 panels. Indeed, from the early 1970s on, CICS applications were often written for the 3270. Various versions of Wylbur have support for 3270, including support for full-screen applications. McGill University's MUSIC/SP operating system provided support for 3270 terminals and applications, including

4158-560: Was determined by the programming of a plugboard inside the back of the machine. Soft keys date to avionics multi-function displays of military planes of the late 1960s/early 1970s, such as the Mark II avionics of the F-111D (first ordered 1967, delivered 1970–1973). In computing use, they were found on the HP 9810A calculator (1971) and later models of the HP 9800 series , which featured 10 programmable keys in 5×2 block (2 rows of 5 keys) at

4224-563: Was still used at Michigan well into the 1990s. Many manufacturers, such as GTE , Hewlett-Packard , Honeywell /Incoterm Div, Memorex , ITT Courier , McData , Harris, Alfaskop and Teletype / AT&T created 3270 compatible terminals, or adapted ASCII terminals such as the HP 2640 series to have a similar block-mode capability that would transmit a screen at a time, with some form validation capability. The industry distinguished between 'System compatible controllers' and 'Plug compatibility controllers', where 'System compatibility' meant that

4290-463: Was the successor to the IBM 2260 display terminal. Due to the text color on the original models, these terminals are informally known as green screen terminals. Unlike a character-oriented terminal , the 3270 minimizes the number of I/O interrupts required by transferring large blocks of data known as data streams , and uses a high speed proprietary communications interface, using coaxial cable . IBM no longer manufactures 3270 terminals, but

4356-595: Was widely used as an IBM mainframe terminal before PCs became commonly used for the purpose. It was part of the 3270 series, using the 3270 data stream . Terminals could be connected to a 3274 controller, either channel connected to an IBM mainframe or linked via an SDLC ( Synchronous Data Link Control ) link. In the Systems Network Architecture (SNA) protocol these terminals were logical unit type 2 (LU2). The basic models 2A and 3A used red, green for input fields, and blue and white for output fields. However,

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