IBM 3270 PC

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IBM 3270 PC (System Unit 5271)
IBM 3270 PC with 122-key keyboard and 5272 colour monitor.
Type Personal computer
Release date October 1983; 35 years ago (1983)
Discontinued 1987 (1987)
Operating system 3270-PC Control Program with PC DOS 2.0 or 2.1
IBM 3270 Workstation Program with PC DOS 3.3
CPU Intel 8088 @ 4.77 MHz
Memory 256KB ~ 640KB

The IBM 3270 PC (IBM System Unit 5271), released in October 1983, was an IBM PC XT containing additional hardware which could emulate the behaviour of an IBM 3270 terminal. It could therefore be used both as a standalone computer, and as a terminal to a mainframe.

IBM later released the 3270 AT (IBM System Unit 5273), which was a similar design based on the IBM PC AT. They also released high-end graphics versions of the 3270 PC in both XT and AT variants. The XT-based versions were called 3270 PC/G and 3270 PC/GX and they used a different System Unit 5371, while their AT counterparts (PC AT/G and PC AT/GX) had System Unit 5373.[1]


The additional hardware occupied nearly all the free expansion slots in the computer. It included a video card which occupied 1-3 ISA slots (depending on what level of graphics support was required), and supported CGA and MDA video modes. The display resolution was 720×350, either on the matching 14-inch color monitor (model 5272)[2] or in monochrome on an MDA monitor.

A further expansion card intercepted scancodes from the 122-key 3270 keyboard, translating them into XT scancodes which were then sent to the normal keyboard connector. This keyboard, officially called the 5271 Keyboard Element, weighed 9.3 pounds.[2]

The final additional card (a 3278 emulator) provided the communication interface to the host mainframe.[2]


  • 3270 PC (System Unit 5271) - original 3270 PC, initially offered in three different Models numbered 2, 4, and 6. Model 2 had non-expandable memory of 256 KB and a single floppy drive. Model 4 had expandable memory, a second floppy drive, and a parallel port. Model 6 replaced one of the floppy drives with a 10 MB hard disk.[3] Model 6 had a retail price of $6,210 at its launch (with 512KB RAM), not including display, cables and software; a working configuration with an additional 192KB RAM, color display (model 5272) and the basic cabling and software (but without support for host/mainframe-side graphics) ran to $8,465.[2] A 1985 review by PC Magazine found that fast file transfer to and form the mainframe was the strong selling point of this unit: file transfers that took hours with an Irma board took only minutes with the boards (and software) that came with the 3270 PC. The 3270 PC suffered however from incompatibility problems with other XT hardware and DOS software[2] (for example, Microsoft QuickBasic[4]). Its 3278 mainframe board was also considered lackluster, in comparison with an IBM 3279 graphics terminal, because it provided only a 24-line display during mainframe sessions, requiring either PC-side scrolling for the 32-line applications typically used with a 3279, or explicit 24-line application support on the mainframe side.[2]
    • later released Models 24 (two floppy drives) and 26 (floppy plus 10 MB hard-disk) supported and were bundled with the IBM 3295 Plasma Monitor. This monochrome display was intended to provide a high-capacity text terminal for simultaneous mainframe sessions. It had two sets of fonts: one with 6x12-pixel characters, with which it could display text in 62 rows by 160 columns, and a larger font with 9x16-pixel characters, with which it could display 46 rows by 106 columns of text.[5][1]
    • Models 30, 50, and 70 came with 640 KB RAM on the system board, and followed same disk pattern as the initial models (one floppy, two floppies, and floppy plus hard drive) but with a 20 MB hard disk. They (and all subsequent models) also reverted to the 5151/5272 Display Adapter (no Plasma Monitor support).[1]
    • Models 31, 51, and 71 reverted to 256 KB RAM on the system board but were also shipped with an Expanded Memory Adapter (XMA) with 1 MB RAM standard.[1] Optionally these models (released in 1986) could be equipped with up to 2 MB of XMA.[6][7]
    • Models P30/P50/P70 and P31/P51/P71 were like Models 30/50/70 and respectively 31/51/71 but with a 101-key (AT-style) keyboard replacing the 5271 Keyboard.[1]

Models 31/51/71 and all P-models, required version 3.0 of the Control Program.[1]

  • 3270 PC/G - 3270 PC with improved graphics hardware and mouse support; it was sold together with an IBM 5279 Color Display, which was powered by an IBM 5278 Display Attachment Unit All Points Addressable (APA) graphics card providing 720x512 resolution and CGA emulation for compatibility. At its launch, the retail price for this configuration was $11,240.[2]
    • initially offered as Model 12, 14, and 16; these had similar disk configuration options (one floppy, two floppies, and one floppy plus on hard disk) as the basic 3270 PC, but had more standard memory at 384 KB, 512, and respectively 576 KB. Even the basic Model 12 had a parallel port and supported a mouse. The mouse (IBM 5277) was optional though even for Model 16, and had a list price of $340.[3]
    • 3270 PC/GX - Extended APA graphics support (1024x1024) provided by the IBM 5378 Display Attachment Unit; shipped with a 19-inch color or monochrome monitor (IBM 5379). Price at launch was $18,490, although adding the basic software and cables ran close to $20,000.[2]

The basic 3270 PC could not be upgraded to the PC/G or PC/GX. These two models used a different basic unit (System Unit 5371), itself priced at $6,580 (for Model 16) without graphics.[2][3]

Later, AT-based models:

  • 3270 AT (System Unit 5273) - corresponds to the 3270 PC, but based on an IBM AT.
  • 3270 AT/G and GX (System Unit 5373) - corresponds to the 3270 PC/G and PC/GX, respectively, but based on an IBM AT.


At its launch, the 3270 PC used the 3270 PC Control Program as its operating system. PC DOS 2.0 (and later 2.1) could run as a task under the Control Program. Only one PC DOS task could be run at any given time, but in parallel with this, the Control Program could run up to four mainframe sessions. The Control Program also provided a basic windowing environment, with up to seven windows; besides the four mainframe and one DOS session, it also provided two notepads. The notepads could be used to copy text from the PC DOS session to the mainframe sessions but not vice versa. Given the small size of the character display, a review by PC Magazine concluded that the windowing features were hardly useful, and the notepads even less so. The Control Program was also described as a "memory hog" in this review, using about 200 KB of RAM in a typical configuration.[2] More useful were the specialized PC DOS file transfer utilities that were available (called simply SEND and RECEIVE), which allowed files to be exchanged with the mainframe and provided ASCII/EBCDIC conversion.[2] The list prices for the Control Program and file transfer utilities were $300 and $600, respectively.[3] At the launch of the 3270 PC, the Control Program was the distinguishing software feature between a 3270 PC and an XT with an added 3278 board.[8]

IBM considered the 3270 PC Control Program to be mainframe software, so it did not provide user-installable upgrades. Upgrades had to be installed by expert system programmers.[2]

The PC/G and PC/GX models ran a mainframe-graphics-capable version of the Control Program called the Graphics Control Program (GCP). On the mainframe side, the IBM Graphical Data Display Manager (GDDM) release 4 (and later) was compatible with these two workstations. The GDDM provided support for local pan and zoom (without taxing the host mainframe) on the PC/G and PC/GX.[9]

In 1987 IBM released the IBM 3270 Workstation Program, which supported both XT and AT models of the 3270 PCs, as well as the plain XT and AT models (even with an XT or AT keyboard) with a 3278 board. It allowed up to six concurrent DOS 3.3 sessions, but the number of mainframe sessions and notepads remained the same (four and two, respectively).[10][11]


BYTE in 1984 praised the 3270 PC's 3278 emulation and color monitor, and concluded that the computer was "a must" for those seeking high-quality graphics or mainframe communications.[12]

See also


  1. ^ a b c d e f Personal Computer Family Service Information Manual (January 1989), IBM document SA38-0037-00, Chapter 10. "3270 PC Products"
  2. ^ a b c d e f g h i j k l Edward A. Valenzuela (January 22, 1985). "3270 PC: All things to all users?". PC Magazine. pp. 157–161 continued on 166–167. ISSN 0888-8507. 
  3. ^ a b c d "IBM Personal Computers At a Glance". BYTE. Fall 1984. pp. 10–26. Retrieved March 18, 2016. 
  4. ^
  5. ^
  7. ^ Staff writers (April 14, 1986). "3270 demand not expected to rise". InfoWorld. p. 5. ISSN 0199-6649. 
  8. ^ BYTE Guide to the IBM PC, fall 1984, p. 35
  9. ^ Eric Bender (July 2, 1984). "IBM bases graphics units on 3270-PC". Computerworld. p. 8. ISSN 0010-4841. 
  10. ^ Belitsos, Byron (April 6, 1987). "Operating System/2 to let PCs integrate more easily into SNA". InfoWorld. p. 6A. ISSN 0199-6649. 
  11. ^
  12. ^ Augustin, Larry (Fall 1984). "The Mainframe Connection: IBM's 3270 PC". BYTE. pp. 231–237. Retrieved March 18, 2016. 

External links

  • Detailed technical information about the 3270 PC (basic model, not the PC/G or PC/GX)
  • Full list of 5271 models
  • Scanned documentation on bitsavers
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