IBM 5271 Personal Computer XT
| Company type | Product line |
|---|---|
| Industry | Computer hardware |
| Predecessor | IBM PC XT |
| Founded | October 1983 |
| Founder | IBM |
| Fate | Discontinued |
| Successor | IBM 3270 AT and variants |
| Headquarters | United States |
Area served | Worldwide |
| Products | IBM 3270 PC, 3270 AT, 3270 PC/G, 3270 PC/GX, 3270 AT/G, 3270 AT/GX |
| Owner | IBM |
| Parent | IBM |
The IBM 3270 PC (System Unit 5271), introduced by IBM in October 1983, is a personal computer primarily derived from the IBM PC XT architecture but enhanced to simulate an IBM 3270 terminal. This hybrid design allows it to operate both as an independent PC and as a terminal connected to a Mainframe computer.
Subsequently, IBM launched the 3270 AT (System Unit 5273), built on the IBM PC AT platform, alongside advanced graphics variants for both XT and AT models: the XT-based 3270 PC/G and PC/GX (System Unit 5371), as well as their AT equivalents, the PC AT/G and PC AT/GX (System Unit 5373).
Technology
Most expansion slots are occupied by additional components, including a video card that can use between one and three ISA slots depending on graphical requirements. This card supports both CGA and MDA modes, delivering a resolution of 720×350 pixels on either a dedicated 14-inch color display (model 5272) or an MDA monitor.
Another expansion board converts scancodes generated by the hefty (9.3 lb) 122-key 5271 Keyboard Element into XT-compatible scancodes for the standard keyboard interface.
A separate card is responsible for emulating the 3278 terminal, facilitating communication with the host mainframe system.
Models
- 3270 PC (System Unit 5271) – Originally available in Models 2, 4, and 6:
- Model 2: featured fixed memory at 256 KB with a single floppy disk drive and no expandability.
- Model 4: offered expandable memory, dual floppy drives, and included a parallel port.
- Model 6: replaced one floppy drive with a 10 MB hard disk. This model debuted at approximately , with 512 KB RAM excluding display and software; a fully equipped configuration with color monitor and extra RAM cost around . The system was noted for rapid file transfers to mainframes compared to rivals but had compatibility challenges with other XT hardware and DOS applications. Its mainframe interface supported only a 24-line display, restricting usability with standard 32-line software.
- Subsequent models:
- Models 24/26 introduced support for the monochrome IBM 3295 Plasma Monitor, enabling high-capacity text displays up to 62x160 characters.
- Models 30/50/70 upgraded system memory to 640 KB and incorporated larger hard drives of up to 20 MB but reverted to conventional display adapters without Plasma Monitor compatibility.
- Models 31/51/71 returned to 256 KB RAM but included a standard Expanded Memory Adapter (XMA), allowing up to an additional 2 MB of RAM.
- P-series models replaced the original keyboard with a modernized 101-key AT-style keyboard, requiring Control Program version 3.0.
- 3270 PC/G – Featured enhanced graphics hardware with optional mouse support, bundled with IBM’s color IBM 5279 Display driven by an IBM 5278 APA graphics adapter providing a resolution of 720×512 pixels alongside CGA emulation. Initial pricing was about . These were offered as Models 12,14,16 with improved memory options and integrated parallel ports; the mouse was available separately for .
- 3270 PC/GX – Offered extended APA graphics capabilities with higher resolution (1024×1024) through IBM’s Display Attachment Unit (5378), paired with larger IBM 5379 color or monochrome monitors. Launch prices approached , reaching nearly when fully configured.
The original basic 3270 PC could not be upgraded to G or GX versions due to incompatible system units priced around without graphics capability.
Later models based on the AT architecture included:
- 3270 AT (System Unit 5273) – an AT-based counterpart to the original model.
- 3270 AT/G and AT/GX (System Unit 5373) – AT-based versions corresponding to the PC/G and PC/GX models respectively.
Software
When initially released, the 3270 PC operated using the 3270 PC Control Program as its system software. Under this Control Program, PC DOS version 2.0 (and later 2.1) could run as a single task, alongside up to four simultaneous mainframe sessions. The Control Program provided a simple windowing interface supporting up to seven windows: four dedicated to mainframe sessions, one for DOS, and two notepads. These notepads facilitated copying text from the DOS environment to mainframe sessions, although the reverse was not supported. A review by PC Magazine highlighted that the windowing capabilities were somewhat limited and described the Control Program as a "memory hog," utilizing approximately 200 KB of RAM. More practical were the PC DOS file transfer utilities ( and ), which enabled file exchanges between the PC and mainframe systems, including conversions between ASCII and EBCDIC formats. The pricing for the Control Program and these file transfer utilities was roughly and , respectively. At its debut, the Control Program clearly differentiated the 3270 PC from an XT equipped with a 3278 board.
IBM categorized the Control Program as mainframe software; consequently, updates had to be performed by skilled system programmers rather than being user-installable.
The PC/G and PC/GX variants featured a graphics-enabled iteration known as the Graphics Control Program (GCP). On the mainframe side, IBM's Graphical Data Display Manager (GDDM) version 4 and subsequent releases supported these models, allowing local pan and zoom operations without imposing additional load on the host mainframe.
In 1987, IBM launched the IBM 3270 Workstation Program, compatible with XT and AT versions of the 3270 PCs as well as standard XT and AT machines fitted with a 3278 board. This software permitted up to six simultaneous DOS 3.3 sessions while maintaining four concurrent mainframe sessions and two notepads.
Reception
In 1984, BYTE magazine commended the 3270 PC for its effective 3278 emulation and color display, concluding that it was essential for users requiring superior graphics or robust mainframe connectivity.