IBM 3270 PC

IBM 3270 PC (System Unit 5271)
Type Personal computer
Release date October 1983 (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]


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

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:


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. 1 2 3 4 5 6 Personal Computer Family Service Information Manual (January 1989), IBM document SA38-0037-00, Chapter 10. "3270 PC Products"
  2. 1 2 3 4 5 6 7 8 9 10 11 12 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. 1 2 3 4 "IBM Personal Computers At a Glance". BYTE. Fall 1984. pp. 10–26. Retrieved March 18, 2016.
  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.
  12. Augustin, Larry (Fall 1984). "The Mainframe Connection: IBM's 3270 PC". BYTE. pp. 231–237. Retrieved March 18, 2016.

External links

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