IBM 3270 PC
| Company type | Personal computer |
|---|---|
| Industry | Computer hardware |
| Predecessor | IBM PC XT |
| Founded | October 1983 |
| Headquarters | Armonk , United States |
| Products | IBM 3270 PC, IBM 3270 AT, 3270 PC/G, 3270 PC/GX, 3270 AT/G, 3270 AT/GX |
The IBM 3270 PC (System Unit 5271), introduced in October 1983 by IBM, is a personal computer that integrates conventional PC XT hardware with specialized components and software designed to emulate an IBM 3270 terminal. This hybrid design enables it to function either as an independent PC or as a terminal linked to a mainframe system.
Subsequently, IBM released the 3270 AT (System Unit 5273), which is built upon the IBM PC AT architecture, alongside advanced graphics versions for both XT and AT platforms. The XT-based graphics editions—3270 PC/G and 3270 PC/GX—utilize System Unit 5371, whereas the AT-based variants—PC AT/G and PC AT/GX—are equipped with System Unit 5373.
Technology
Most of the expansion slots are occupied by additional hardware, including a video card that spans between one and three ISA slots. This card supports both CGA and MDA modes, delivering a resolution of 720×350 pixels on either the IBM 14-inch color monitor (model 5272) or an MDA display.
Another expansion card translates scancodes from the specialized 122-key IBM keyboard (5271 Keyboard Element) into standard XT scancodes to ensure compatibility. A third card emulates a 3278 terminal, handling communications with the host mainframe.
Models
- 3270 PC (System Unit 5271) – Originally available in Models 2, 4, and 6:
- Model 2: featured non-expandable 256 KB memory and a single floppy drive.
- Model 4: offered expandable memory, dual floppy drives, and a parallel port.
- Model 6: replaced one floppy drive with a 10 MB hard disk.
At launch, Model 6 was priced around (512KB RAM), excluding display and software; a fully equipped setup including color display and additional RAM could reach approximately . A review in PC Magazine praised its rapid mainframe file transfer but pointed out incompatibilities with certain XT hardware and DOS applications, such as Microsoft QuickBasic. The mainframe interface was limited to a 24-line display, restricting compatibility with standard 32-line programs.
Later iterations included:
- Models 24 and 26, which incorporated the IBM 3295 Plasma Monitor to enhance text display across multiple mainframe sessions.
- Models 30, 50, and 70 increased onboard RAM to 640 KB and upgraded hard drives to 20 MB but discontinued support for the Plasma Monitor.
- Models 31, 51, and 71 reduced onboard RAM back to 256 KB but added an Expanded Memory Adapter (XMA) supporting up to 2 MB of RAM.
- P-series models mirrored these configurations but replaced the original IBM keyboard with a standard AT-style 101-key keyboard.
Starting from model P31, Control Program version 3.0 was required.
- 3270 PC/G – A graphics-enhanced model paired with the IBM 5279 Color Display and powered by the IBM 5278 Display Attachment Unit APA graphics card, delivering a resolution of 720×512 pixels with CGA emulation. Initial models (12,14,16) featured increased memory ranging from 384 KB to 576 KB, included a parallel port, and offered optional mouse support. The launch price was approximately .
- 3270 PC/GX – Offered extended APA graphics capabilities up to a resolution of 1024×1024 via the IBM5378 Display Attachment Unit; shipped with either a 19-inch color or monochrome monitor (IBM5379). Pricing at release was about , rising close to when bundled with software and cables.
The original IBM3270 PC could not be upgraded to either G or GX models because they utilized different system units priced around , excluding graphics.
Later models based on the AT architecture include:
- 3270 AT (System Unit5273) – An AT-based version corresponding to the original3270 PC.
- 3270 AT/G and GX (System Unit5373) – The AT-based equivalents of the PC/G and PC/GX models respectively.
Software
Upon its release, the 3270 PC operated using the 3270 PC Control Program as its primary operating system. It was capable of running PC DOS 2.0 (and later 2.1) as a task within this environment; however, only a single DOS task could be active at any given time, alongside up to four simultaneous mainframe sessions. The Control Program provided a rudimentary windowing interface featuring seven distinct windows: four dedicated to mainframe sessions, one for DOS, and two functioning as notepads. These notepads permitted users to transfer text from the DOS session into mainframe sessions but did not support copying in the opposite direction. Due to the limited screen size, PC Magazine regarded these windowing capabilities as somewhat constrained and criticized the Control Program for its substantial memory usage, requiring roughly 200 KB of RAM. More significant were specialized PC DOS file transfer tools ( and ), which facilitated file sharing between the PC and mainframes while handling ASCII and EBCDIC code conversions. The Control Program and these file transfer utilities were priced at approximately and , respectively. This suite of software set the 3270 PC apart from a standard XT equipped with a 3278 adapter at launch.
IBM categorized the Control Program as mainframe software, meaning that updates necessitated professional installation rather than user-performed upgrades.
The PC/G and PC/GX variants utilized an enhanced graphics-capable edition known as the Graphics Control Program (GCP). On the mainframe end, IBM's Graphical Data Display Manager (GDDM) version 4 and subsequent releases supported these models, allowing local pan and zoom functions without imposing additional load on the host mainframe.
In 1987, IBM released the 3270 Workstation Program, compatible with both XT and AT versions of the 3270 PC as well as standard XT and AT machines fitted with a 3278 board. This software enabled up to six simultaneous DOS 3.3 sessions while still supporting four mainframe connections and two notepad windows.
Reception
In 1984, BYTE magazine commended the 3270 PC for its effective 3278 emulation and vibrant color display, ultimately recommending it as essential for users requiring superior graphics or robust mainframe communication capabilities.