IBM 3270

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The IBM 3270 is a family of block oriented[1] display and printer computer terminals introduced by IBM in 1971[2] and normally used to communicate with IBM mainframes. The 3270 was the successor to the IBM 2260 display terminal.[3] Due to the text colour 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 the IBM 3270 protocol is still commonly used[4] via TN3270[5] 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.[2] The main goal of the system was to maximize 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.

Sample IBM 3270 cluster with one control unit connected to a printer and two displays

3270 devices are clustered, with one or more displays or printers connected to a control unit (the 3275 and 3276 included an integrated control unit).[6] 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 a line.

In a data stream, both text and control (or formatting functions) are interspersed allowing an entire screen to be "painted" as 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,[a] highlighting, character set,[a] 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[a] character attributes associated with individual screen locations.

Using a technique known as "read modified",[7] 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 is also a "read buffer"[8] 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 a 78 key version with twelve. Both versions had two Program Attention (PA) keys.[9][10] The data entry keyboard had five PF keys and two PA keys. The operator console keyboard had twelve PF keys and two PA keys.[11]:p.19 Later 3270s had an Attention[b] key, a Cursor Select[c] 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[d] to 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 porting of Lotus 1-2-3 to mainframes with 3279 screens did not meet with success because its programmers were not able to properly adapt 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.[12] IBM and third-party software that included an interactive component took for granted 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[13] 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.

The SPF and Program Development Facility (ISPF/PDF) editors for MVS and VM/SP (ISPF/PDF 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.

Various versions of Wylbur have support for 3270, including support for 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 the PROFS calendar was the most commonly displayed screen on office terminals around the world.[citation needed]

A version of the WordPerfect word processor ported to System/370 was designed for the 3270 architecture.

Third parties[edit]

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.[clarification needed] MTS was the default OS at Michigan for many years, and was still used at Michigan well into the 1990s. Many manufacturers, such as GTE, Hewlett Packard, Honeywell/Incoterm Div, Memorex, ITT Courier and Teletype/AT&T created 3270 compatible[e] 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. Modern applications are sometimes built upon legacy 3270 applications, using software utilities to capture (screen scraping) screens and transfer 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.[citation needed]


The IBM 3270 display terminal subsystem consists of displays, printers and controllers. Optional features for the 3275 and 3277 are the selector-pen or light 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.[11] 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 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.

CUT vs. DFT[edit]

There are two types of 3270 displays in respect to where 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. For DFT (Distributed Function Terminal) type displays, most of the 3270 data stream is forwarded to the display by the controller. The display interprets the 3270 protocol itself.

Display Station Name CUT vs. DFT
3178 - all models CUT
3179 - Model 1 CUT
3179 - Models G1, G2 DFT
3180 Model 1 CUT
3191 - all models CUT
3192 - Models C, D, F, L, W CUT
3192 - Model G DFT
3193 - all models DFT
3194 - all models DFT
3277 - all models CUT
3278 - all models CUT
3279 - all models CUT
3290 - all models DFT


  • 3277 model 1: 40×12 terminal
  • 3277 model 2: 80×24 terminal, the biggest success of all
  • 3277 GA: a 3277 with an RS232C I/O, often used to drive a Tektronix 4013 or 4015 graphic screen (monochrome)


  • 3278 models 1–5: next-generation, with accented characters and dead keys in countries that needed them
    • model 1: 80x12
    • model 2: 80×24
    • model 2A: 80x24 (console) with 4 lines reserved
    • model 3: 80×32 or 80x24 (switchable)
    • model 4: 80×43 or 80x24 (switchable)
    • model 5: 132×27 or 80×24 (switchable)
  • 3278 PS: programmable characters; able to display monochrome graphics


IBM 3279 Colour Display Terminal
An Informatics General computer programmer using an IBM 3279 terminal

The IBM 3279 was IBM's first colour[14] terminal. IBM initially announced four models, and later added a fifth model for use as a processor console.

  • Models
    • model 2A: 80-24 base color
    • model 2B: 80-24 extended color
    • model 2C: 80-24 base color (console) with 4 lines reserved
    • model 3A: 80-32 base color
    • model 3B: 80-32 extended color
  • Base color
    In base color mode the protection and intensity field attributes determine the color:
Base color mode
Protection Intensity Color
Unprotected Normal


Unprotected Intensified


Protected Normal


Protected Intensified


  • Extended color
    In extended color mode the color field and character attributes determine the color as one of
    • Neutral (White)
    • Red
    • Blue
    • Green
    • Pink
    • Yellow
    • Turquoise

The 3279 was introduced in 1979.[15] The 3279 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.[16] 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 model 2 used red, green for input fields, and blue and white for output fields. However, there were other models with seven colors and different screen sizes, and one kind had a loadable character set that could be used to show graphics.

The IBM 3279 with its graphics[f] software support, Graphical Data Display Manager (GDDM), was designed at IBM's Hursley Development Laboratory, near Winchester, England.[17]


  • 3290 Information Panel: a large, amber monochrome plasma display unit announced[18] 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.[19][g] 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 partions (logical screens).


  • 3178: lower cost terminal (1983)
  • 3179: low cost colour terminal (1984)


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 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.


  • Model C provides a 7-color 14 inch CRT with 80x24 or 80x32 characters
  • Model D provides a green monochrome 15 inch CRT with 80x24, 80x32, 80x44 or 132x27 characters
  • Model F provides a 7-color high-resolution 14 inch CRT with 80x24, 80x32, 80x44 or 132x27 characters
  • Model G provides a 7-color 14 inch CRT with 80x24 or 80x32 characters
  • Model L provides a green monochrome 15 inch CRT with 80x24, 80x32, 80x44 or 132x27 characters with a selector light pen capability
  • Model W provides a black and while 15 inch CRT with 80x24, 80x32, 80x44 or 132x27 characters


The IBM 3193 Display Station 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 a 1.44MB 3.5" floppy drive and IND$FILE transfer.

  • Model C provides a 12 inch color CRT with 80x24 or 80x32 characters
  • Model D provides a 15 inch monochrome CRT with 80x24, 80x31, 80x44 or 132x27 characters
  • Model H provides a 14 inch color CRT with 80x24, 80x31, 80x44 or 132x27 characters


  • 3104: low-cost R-loop connected terminal for the IBM 8100 system
  • 3472 Infowindow

Informer 270 376/SNA[edit]

The Informer company manufactured a special version of their model 270 terminal that was compatible with IBM 3270 and it's associated coax port to connect to a 3x74.[20][21]


  • 3275 remote display with controller function (no additional displays up to one printer)
  • 3276 remote display with controller function (up to a limited number of displays or printers)


  • 3284 matrix printer
  • 3286 matrix printer
  • 3287 printer, including a colour model
  • 3288 line printer
  • 3268-1 : R-loop connected stand-alone printer for the IBM 8100 system


  • 3271 remote controller
  • 3272 local controller
  • 3274 cluster controller (different models could be channel-attached or remote via BSC or SDLC communication lines, and had between eight and 32 co-ax ports)
  • 3174 cluster controller

By 1994 the "3174 Establishment Controller" supported features such as attachment to multiple hosts via Token Ring, Ethernet, or X.25 in addition to the standard channel attach or SDLC, and terminal attachment via twisted pair, Token Ring or Ethernet in addition to co-ax. They also support attachment of asynchronous ASCII terminals, printers, and plotters alongside 3270 devices.[22]

Non-IBM Controllers[edit]

An alternative implementation of an establishment controller exists in form of OEC (Open Establishment Controller).[23][24][25][26] It's a combination of an Arduino shield with a BNC connector and a Python program that runs on a POSIX system. OEC allows to connect a 3270 display to IBM mainframes via TN3270 or to other systems via VT100. Currently only CUT but not DFT displays are supported.


IBM offered a device called 3299 that acted as a multiplexer between an accordingly configured 3x74 and several displays, therefore increasing the number of displays a single controller could serve with the added benefit of extending the maximum distance between controller and displays as the signal was terminated and re-established by the 3299.

The 3299 model 2 multiplexed a single physical connection to a controller to 8 displays.

Graphics models[edit]

These were specialized models that provided All Points Addressable (APA) graphics, allowing more efficient graphics than the older technique of piecing together custom symbols defined using the Programmable Symbol Sets (PSS) feature. The 3179G, 3279G and 3472G were APA graphics models.

IBM 3179G[edit]

IBM 3179G
Also known asIBM 3179G Color Display Station
Release dateMarch 1984 (1984-03)
Introductory priceUS$2,295 (equivalent to $5,648 in 2019)

The IBM 3179G released in March 1984[27] is an IBM mainframe computer terminal providing 80×24 or 80×32 characters plus graphics.[28][29][30][31][32]

3179-G terminals combine text and graphics as separate layers on the screen. Although the text and graphics appear combined on the screen, the text layer actually sits over the graphics layer. The text layer contains the usual 3270-style cells which display characters (letters, numbers, symbols, or invisible control characters).[33] The graphics layer is an area of 720×384 pixels.[34] 'All Points Addressable' or 'vector graphics' is used to paint each pixel in one of sixteen colors. As well as being separate layers on the screen, the text and graphics layers are sent to the display in separate data streams, making them completely independent.

The G10 model is a standard 122-key typewriter keyboard, while the G20 model offers APL on the same layout. Compatible with IBM System/370, IBM 4300 series, 303x, 308x, IBM 3090, and IBM 9370.

IBM 3279G[edit]

The 3279g has a capability called "Extended Data Stream" (EDS). Documentation for the SAS software package says "The ability to do graphics on a 3270 terminal implies that it is an EDS device."[35]

IBM 3472G[edit]

The IBM 3472G has Native Vector Graphics capability.[33]


The IBM 3270 display terminal subsystem was designed and developed by IBM's Kingston, New York, laboratory (which later closed during IBM's difficult time in the mid-1990s). The printers were developed by the Endicott, New York, laboratory. As the subsystem expanded, the 3276 display-controller was developed by the Fujisawa laboratory, Japan, and later the Yamato laboratory; and the 3279 color display and 3287 color printer by the Hursley, UK, laboratory. The subsystem products were manufactured in Kingston (displays and controllers), Endicott (printers), and Greenock, Scotland, UK, (most products) and shipped to users in U.S. and worldwide. 3278 terminals continued to be manufactured in Hortolândia, near Campinas, Brazil as far as late 1980s, having its internals redesigned by a local engineering team using modern CMOS technology, while retaining its external look and feel.[citation needed]

Telnet 3270[edit]

Telnet 3270, or tn3270 describes both the process of sending and receiving 3270 data streams using the telnet protocol and the software that emulates a 3270 class terminal that communicates using that process.[5][36] tn3270 allows a 3270 terminal emulator to communicate over a TCP/IP network instead of an SNA network. Telnet 3270 can be used for either terminal or print connections. Standard telnet clients cannot be used as a substitute for tn3270 clients, as they use fundamentally different techniques for exchanging data.

Technical Information[edit]

3270 character set[edit]

The 3270 displays are available with a variety[37] of keyboards and character sets. The following table shows the 3275/3277/3284/3286 character set[38][39] for US English EBCDIC (optional characters were available for US ASCII, and UK, French, German, and Italian EBCDIC). The numbers are the equivalent Unicode code points.

On the 3275 and 3277 terminals without the a text feature, lower case characters display as uppercase. NL, EM, DUP, and FM control characters display and print as 5, 9, *, and ; characters, respectively, except by the printer when WCC or CCC bits 2 and 3 = '00'b, in which case NL and EM serve their control function and do not print.[11]:p.15

3270 Character Set (US EBCDIC)
_0 _1 _2 _3 _4 _5 _6 _7 _8 _9 _A _B _C _D _E _F
0_ NUL
1_ DLE
2_ ETB
3_ SYN
4_ SP
5_ &
6_ -
7_ :
8_ a
9_ j
A_ s
C_ A
D_ J
E_ S
F_ 0

  Letter  Number  Punctuation  Symbol  Other  Undefined

Data stream[edit]

Data sent to the 3270 consist of commands, a Copy Control Character (CCC)[h] or Write Control Character (WCC) if appropriate, a device address[h] for copy, orders, character data and[a] structured fields. Commands instruct the 3270 control unit to perform some action on a specified device, such as a read or write. Orders are sent as part of the data stream to control the format of the device buffer. Structured fields are to convey additional control functions and data to or from the terminal.[a]

On a local non-SNA controller, the command is a CCW opcode rather than the first byte of the outbound display stream; on all other controllers, the command is the first byte of the display stream, exclusive of protocol headers.


The following table includes datastream commands and CCW opcodes for local non-SNA controllers; it does not include CCW opcodes for local SNA controllers.

3270 commands[40]
Command Hexadecimal Graphic Function
Copy[h] n/a F7 37 7 Copy from one device buffer to another, e.g., from a display to a printer
Erase All Unprotected[41] 0F 6F 3F ? Erase all unprotected fields and reset modified data tags
Erase/Write[42] 05 F5 35 5 Erase device buffer, then write WCC folloed by orders and data
Erase/Write Alternate[i][43] 0D 7E 3D = Erase device buffer, set alternate size, then write WCC folloed by orders and data
No Operation 03 n/a n/a n/a May be used to retrieve pending status
Read Buffer[44] 02 F2 22 2 Read entire device buffer, including attributes
Read Modified[45] 06 F6 36 6 Read AID, cursor and, except for short read, modified fields from device
Read Modified All[46] n/a 6E 3E : Read AID, cursor and modified fields from device; no short read
Select[47] 0B n/a n/a n/a Transfer data from device to control unit with channel disconnected
Select RB[j][48] 1B n/a n/a n/a Select Read Buffer;
may only be chained to Read Buffer
Select RBP[j][49] 3B n/a n/a n/a Select Read Buffer from Position;
may only be chained to Read Buffer
Select RM[j][50] DB n/a n/a n/a Select Read Modified
Select RMP[j][51] 2B n/a n/a n/a Select Read Modified from Position
Select WRT[j][52] 4B n/a n/a n/a Select WRT Command
May only be chained to a Write or Write Structured Field
Sense[53] 04 n/a n/a n/a Retrieve error information after unit check
Sense ID[i][54] E4 n/a n/a n/a Retrieve control unit identification
Write[55] 01 F1 31 1 Write WCC followed by orders and data
Write Structured Field[i][a][56] 11 F3 n/a 3 Write Structured Field
For remote 3270s non-significant bits are set so that the command forms a valid EBCDIC (or ASCII) character.

Write control character[edit]

The data sent by Write or Erase/Write consists of the command code itself followed by a Write Control Character (WCC) optionally followed by a buffer containing orders or data (or both). The WCC controls the operation of the device. Bits may start printer operation and specify a print format. Other bit settings will sound the audible alarm if installed, unlock the keyboard to allow operator entry, or reset all the Modified Data Tags in the device buffer.


Orders[57] consist of the order code byte followed by zero to three bytes of variable information.

Orders for 3277[k]
Order Hexadecimal code (EBCDIC) Description[11]
Byte 1 Byte 2 Byte 3 Byte 4
Start Field (SF) 1D Attribute character
(see Attributes)
Indicates the start of a field at the current buffer position and provides its attribute
Set Buffer Address (SBA) 11 Address byte 1 Address byte 2 Specifies a buffer address to become the current buffer position
(see Buffer addressing)
Insert Cursor (IC) 13 Positions the cursor at the current buffer position
Program Tab (PT) 05 Advances the current buffer address to the first position of the next unprotected field
Repeat to Address (RA) 3C Address byte 1 Address byte 2 Character to repeat Stores the character in byte 4 in all buffer locations starting at the current buffer position up to but not including the specified address and sets the current buffer position to the specified address
Erase Unprotected to Address (EUA) 12 Address byte 1 Address byte 2 Fills all unprotected fields with nulls starting at the current buffer position up to but not including the specified address


The 3270 has three[58] kinds of attributes:

Field attributes[edit]

The original 3277 and 3275 displays used an 8-bit field attribute byte[59] of which five bits were used.[11]:p.18

  • Bits 0 and 1 are set so that the attribute will always be a valid EBCDIC (or ASCII) character.
  • Bit 2 is zero to indicate that the associated field is unprotected (operator could enter data) or one for protected.
  • Bit 3 is zero to indicate that this field, if unprotected, could accept alphanumeric input. One indicates that only numeric input is accepted, and automatically shifts to numeric for some keyboards.
  • Bit 4 and 5 operate in tandem:
    • '00'B indicate that the field is displayed on the screen and is not selector-pen detectable.
    • '01'B indicates that the field is displayable and selector-pen detectable.
    • '10'B indicates that the field is intensified (bright), displayable, and selector-pen detectable.
    • '11'B indicates that the field is non-display, non-printable, and not pen detectable. This last can be used in conjunction with the modified data tag to imbed static data on the screen that will be read each time data was read from the device.
  • Bit 7 is the "Modified Data Tag", where '0' indicates that the associated field has not been modified by the operator and '1' indicates that it has been modified. As noted above, this bit can be set programmatically to cause the field to be treated as modified.

Later models include base color: "Base color (four colors) can be produced on color displays and color printers from current 3270 application programs by use of combinations of the field intensify and field protection attribute bits. For more information on color, refer to IBM 3270 Information System: Color and Programmed Symbols, GA33-3056."[59]:1–7

Extended attributes[edit]

The 3278 and 3279 and later models used extended attributes[60] to add support for seven colours, blinking, reverse video, underscoring, field outlining, field validation, and programmed symbols.

Character attributes[edit]

The 3278 and 3279 and later models allowed attributes on individual characters[61] in a field to override the corresponding field attributes.

Buffer addressing[edit]

3270 displays and printers have a buffer containing one byte for every screen position. For example, a 3277 model 2 featured a screen size of 24 rows of 80 columns for a buffer size of 1920 bytes. Bytes are addressed from zero to the screen size minus one, in this example 1919. "There is a fixed relationship between each ... buffer storage location and its position on the display screen."[11]:p.13 Most orders start operation at the "current" buffer address, and executing an order or writing data will update this address. The buffer address can be set directly using the Set Buffer Address (SBA) order, often followed by Start Field or Start Field Extended. For a device with a 1920 character display a twelve bit address is sufficient. Later 3270s with larger screen sizes use fourteen or sixteen bits.

Addresses are encoded within orders in two bytes.[62] For twelve bit addresses the high order two bits of each byte are set to form valid EBCDIC (or ASCII) characters. For example, address 0 is coded as X'4040', or space-space, address 1919 is coded as X'5D7F', or ')"'.[11]:pp.75–90 Programmers hand-coding panels usually keep the table of addresses from the 3270 Component Description or the 3270 Reference Card handy. For fourteen and sixteen-bit address, the address uses contiguous bits in two bytes.


The following data stream writes an attribute in row 24, column 1, writes the (protected) characters '> ' in row 24, columns 2 and 3, and creates an unprotected field on row 24 from columns 5-79. Because the buffer wraps around an attribute is placed on row 24, column 80 to terminate the input field. This data stream would normally be written using an Erase/Write command which would set undefined positions on the screen to '00'x. Values are given in hexadecimal.

  Data        Description
  D3          WCC [reset device + restore (unlock) keyboard + reset MDT]
  11 5C F0    SBA Row 24 Column 1
  1D F0       SF/Attribute
              [protected, alphanumeric, display normal intensity, not pen-detectable, MDT off]
  6E 40       '> '
  1D 40       SF/Attribute
              [unprotected, alphanumeric, display normal intensity, not pen-detectable, MDT off]
              SBA is not required here since this is being written at the current buffer position 
  13          IC - cursor displays at current position: Row 24, column 5
  11 5D 7F    SBA Row 24 Column 80
  1D F0       SF/Attribute
              [protected, alphanumeric, display normal intensity, not pen-detectable, MDT off]

Extended Data Stream[edit]

Most 3270 terminals newer than the 3275, 3277, 3284 and 3286 Support an extended data stream (EDS) that allows many new capabilities, including:

  • Display buffers larger than 4096 characters
  • Additional field attributes, e.g., color
  • Character attributes within a field
  • Redefining display geometry
  • Querying terminal characteristics
  • Programmed Symbol Sets
  • All Points Addressable (APA) graphics

See also[edit]


  1. ^ a b c d e f g h When the Structured Field and Attribute Processing Option is available
  2. ^ SNA only, causes an expedited flow attention signal even if the keyboard is locked.
  3. ^ Pressing Cursoe Select has the same effect as clicking a Selector Pen at the current cursor location.
  4. ^ For local non-SNA controllers. If attached to an SNA controller, it initiates a Read Modied or Short AID data transfer. For BSC controllers it causes a positive response to the next poll.
  5. ^ Some, such as the GTE IS/7800, were not fully compatible.
  6. ^ Models 2B and 3B only.
  7. ^ Although the 3290 supports up to 16 explicit partitions, the ISPF SPLIT and SPLITV commands only support 4.
  8. ^ a b c BSC only
  9. ^ a b c Not available on 3271, 3272 or 3275
  10. ^ a b c d e Only available on 3274 D models and 3174
  11. ^ Later models added
    • Start Field Extended (SFE)
    • Modify Field (MF)
    • Set Attribute (SA)
    • Graphic Escape (GE)


3270 Information Display System Introduction (PDF) (Twenty-Third ed.). IBM. October 1988. GA27-2739-22.
3270 Information Display System Data Stream Programmer's Reference (PDF) (Fifth ed.). IBM. December 1988. GA23-0059-4.
IBM 3270 Information Display System Character Set Reference (PDF) (Tenth ed.). IBM. April 1987. GA27 -2837-9.
IBM 3270 Information Display System 3274 Control Unit Description and Programmer's Guide (PDF) (Third ed.). IBM. March 1985. GA23-0061-2.
J. Rekhter (January 1988). Telnet 3270 Regime Option. doi:10.17487/RFC1041. RFC 1041.
Jon Penner (January 1994). TN3270 Current Practices. doi:10.17487/RFC1576. RFC 1576.
Bill Kelly (June 1998). TN3270 Current Practices. doi:10.17487/RFC2355. RFC 2355.
Mykyta Yevstifeyev (June 2011). The 'tn3270' URI Scheme. doi:10.17487/RFC6270. RFC 6270.
  1. ^ 3270Intro.
  2. ^ a b "DPD Chronology 1971". ArchiveIETF. IBM.
  3. ^ "What is 3270 (Information Display System)". 3270 .. over its predecessor, the 2260
  4. ^ "Cleo 3270 Support Documentation". IBM stopped manufacturing .. the IBM 3270
  5. ^ a b RFC2355.
  6. ^ "3270 clusters". Computerworld. May 13, 1985. p. 103.
  7. ^ "Formatted screen input". .. reads a 3270 screen with a read modified command
  8. ^ "Reading from a 3270 terminal". There are two ... , read buffer and read modified.
  9. ^ "Input from a 3270 terminal". PA (Program Attention) key
  10. ^ John Horswill (2000). Designing and Programming CICS Applications. ISBN 1565926765. DFHPA1 is Program Attention (PA) Key 1
  11. ^ a b c d e f g IBM Corporation (1972). IBM 3270 Information Display System Component Description (PDF). GA27-2749-1.
  12. ^ Klaus Brandstaetter. "3270 -Brief History". HOB Techtalk. Retrieved August 19, 2015.
  13. ^ IBM Virtual Machine Facility/370: Terminal User's Guide (PDF) (Seventh ed.), International Business Machines Corporation, October 1974, GC20-1810-6
  14. ^ "Chapter 3. Color Capability", IBM 3270 Information Display System: Color and Programmed Symbols (PDF) (First ed.), International Business Machines Corporation, September 1979, GA33-3056-0
  15. ^ "IBM Archives: 1979".
  16. ^ 3270DS.
  17. ^ "Hardware Products Developed at Hursley (IBM Hursley Museum)".
  18. ^ "Announcement Letter Number". IBM. March 8, 1983. 183-033. Cite journal requires |journal= (help)
  19. ^ 3270Intro, pp. 3-10 – 3-11, 3290 Information Panel.
  20. ^
  21. ^
  22. ^ IBM Corporation (1994). 3174 Establishment Controller/Networking Server Installation Guide (PDF). Archived from the original (PDF) on March 2, 2016.
  23. ^
  24. ^
  25. ^
  26. ^
  27. ^ "IBM 3179 COLOR DISPLAY STATION, Announcement Letter Number 184-039". March 20, 1984. IBM announces the 3179 Color Display Station, a new, low price, color display member of the IBM 3270 Information Display System. The 3179 is a compact, 7-color, 1920-character, 14-inch CRT with bright, clear colors and a smudge-free screen surface. It features a new, modifiable keyboard, and function equivalent to that provided by both the IBM 3279 Models S2A and S2B....First customer shipment for the 3179 is planned for March 1984. ...Purchase...$2,295...
  28. ^ Mark Stephens (June 20, 1988). "Sun Software Emulates IBM Display Terminal". InfoWorld. Vol. 10 no. 25. p. 11. emulates an IBM 3179G display terminal and allows Sun workstation users
  29. ^ Jim Brown (February 16, 1987). "Telex beefs up its lineup". Network World. Vol. 4 no. 7. p. 27. ...The firm also introduced an option that supports attachment of IBM's 3179G Graphic Display Station to a series 274 controller...
  30. ^ Ken Hornstein (January 10, 1991). "IBM 3179G: To beep or not to beep". Newsgroupcomp.terminals.
  31. ^ "Object: 11000554 IBM 3179G, producer: IBM, serial number: 55-N1186, dating: 1985-11-01 - 1985-11-30, received: 2009-11-18, Description: IBM 3179 - Display station (color or graphics) for IBM 3270". Danish Data Historical Society Wiki.
  32. ^ "Software & Services:Productivity Aids". Computerworld. Vol. 19 no. 28. July 15, 1985. p. 62. Pansopic Systems, Inc has announced that Gener/O1, its online program development system for IBM's CICS, now supports IBM's 3179 Model G graphics terminal...
  33. ^ a b Greg Price (January 2008). "3270 Graphics". Prycroft Six. 2. Native Vector Graphics - introduced with the 3179G and also used by the 3192G and 3472G.
  34. ^ "3179G graphics coordinates". Reflection for IBM 14.x - Programming Reference. IBM 3179G graphics coordinates divide the Reflection window into 384 vertical units and 720 horizontal units.
  35. ^ "Terminal Support in the OS/390 Environment".
  36. ^ RFC6270.
  37. ^ 3270CS.
  38. ^ 3270CS, p. 9-2, Figure 9-1. Control Character Assignments (EBCDIC).
  39. ^ 3270CS, p. 9-9, Figure 9-8. English (U.S.) I/O Interface Code (3277, 3286, and 3287).
  40. ^ 3274Desc, p. 1-14, Figure 1-8. Command Codes.
  41. ^ 3270DS, p. 3-7, Erase All Unprotected (EAU) Command.
  42. ^ 3270DS, p. 3-6, Erase/Write Command.
  43. ^ 3270DS, p. 3-6, Erase/Write Alternate Command.
  44. ^ 3270DS, pp. 3-11 – 3-12, Read Buffer Command.
  45. ^ 3270DS, pp. 3-12 – 3-13, Read Modified Command.
  46. ^ 3270DS, pp. 3-13 – 3-14, Read Modified All Command.
  47. ^ 3274Desc, p. 1-70, Select Command (3274 B Units).
  48. ^ 3274Desc, p. 1-71, Select Read Buffer (RB) Command (3274 D Units).
  49. ^ 3274Desc, p. 1-72, Select Read Buffer from Position (RBP) Command (3274 D Units).
  50. ^ 3274D, p. 1-71, Select Read Modified (RM) Command (3274 D Units).
  51. ^ 3274Desc, p. 1-71, Select Read Modified from Position (RMP) Command (3274 D Units).
  52. ^ 3274Desc, p. 1-72, Select WRT Command (3274 D Units).
  53. ^ 3274Desc, p. 1-73, Sense Command (3274 Band D Units).
  54. ^ 3274Desc, p. 1-73, Sense ID Command (3274 Band D Units).
  55. ^ 3270DS, p. 3-5, Write Command.
  56. ^ 3270DS, p. 3-7, Write Structured Field Command.
  57. ^ 3270DS, pp. 44-1 – 4-28, Chapter 4. 3270 Data Stream Orders and Attributes.
  58. ^ 3270DS, pp. 1-6 – 1-9, [1].
  59. ^ a b 3270DS, pp. 1-6 – 1-7, Field Attributes.
  60. ^ 3270DS, p. 1-7, Extended Field Attributes.
  61. ^ 3270DS, pp. 1-7 – 1-9, Character Attributes.
  62. ^ 3270DS, pp. D-1 – D-2, Appendix D. 12-, 14-, and 16-Bit Addressing.

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