IBM 5281 Personal Computer/AT
| Industry | Computer hardware |
|---|---|
| Founded | June 16, 1911 in Endicott, New York, United States |
| Headquarters | Armonk, New York , United States |
| Products | IBM 3270 PC, IBM 3270 AT, IBM 3270 PC/G, IBM 3270 PC/GX, IBM 3270 AT/G, IBM 3270 AT/GX |
The IBM 3270 PC (System Unit 5271), launched in October 1983, is a personal computer created by IBM that merges traditional PC capabilities with the functionality to emulate an IBM 3270 terminal. This design allows it to operate both as an independent computer and as a terminal connected to a mainframe.
Subsequently, IBM released the 3270 AT (System Unit 5273), which was built on the IBM PC AT platform. Alongside this, advanced graphics versions were introduced for both the XT and AT systems: the XT-based 3270 PC/G and PC/GX (System Unit 5371) and the AT-based PC AT/G and PC AT/GX (System Unit 5373).
Technology
Most of the expansion slots were occupied by additional hardware components, including a video card that used up to three ISA slots. This card supported both CGA and MDA display modes at a resolution of 720×350 pixels, which could be viewed on either a dedicated 14-inch color monitor (model 5272) or an MDA-compatible display.
Another expansion card converted signals from the specialized 122-key 5271 Keyboard into XT scancodes, ensuring compatibility with standard PC input. The final board handled communication with the host mainframe by emulating an IBM 3278 terminal.
Models
- 3270 PC (System Unit 5271) — Initially available in Models 2, 4, and 6:
- Model 2: featured fixed 256 KB memory and a single floppy drive without expansion options.
- Model 4: offered expandable memory, two floppy drives, and included a parallel port.
- Model 6: replaced one floppy drive with a 10 MB hard disk; priced around US$6,210 for the version with 512 KB RAM, while fully equipped systems with color monitors and software approached US$8,465.
A review in PC Magazine praised its rapid file transfers to mainframes but mentioned difficulties in compatibility with other XT hardware and DOS applications. The mainframe interface limited display output to 24 lines instead of the usual 32 lines seen in many applications, necessitating certain adjustments.
Subsequent releases included:
- Models 24/26: compatible with the IBM 3295 Plasma Monitor, enabling extended text display.
- Models 30/50/70: upgraded system memory to 640 KB and offered hard drives up to 20 MB.
- Models 31/51/71: reduced base RAM back to 256 KB but incorporated a standard Expanded Memory Adapter (XMA) with optional expansion up to 2 MB.
- P-series variants corresponded to these models but featured a standard AT-style 101-key keyboard.
Control Program version 3.0 became mandatory starting with P-series models.
- 3270 PC/G — Designed for enhanced graphics performance and mouse input, this model came bundled with IBM’s APA graphics adapter (Model 5278) and an IBM 5279 Color Display. Initial pricing was approximately US$11,240.
- Offered in Models 12,14,16 with memory configurations ranging from 384 KB to 576 KB, including parallel ports and optional IBM 5277 mouse support.
- 3270 PC/GX — Provided advanced APA graphics capabilities supporting resolutions up to 1024×1024 pixels through IBM’s Display Attachment Unit (5378). It shipped with larger color or monochrome monitors (IBM 5379). The launch price was near US$18,490; fully equipped systems could cost close to US$20,000.
These graphics-oriented units required separate system units (5371) and were not designed as upgrades from the base model.
Later models based on the AT architecture mirrored these options:
- 3270 AT (System Unit 5273) — The IBM AT counterpart of the original model.
- 3270 AT/G and GX (System Unit 5373) — AT versions of the PC/G and PC/GX graphics configurations.
Software
Upon its release, the 3270 PC operated using the 3270 PC Control Program as its core system software. PC DOS versions 2.0 and later 2.1 could be executed as a single task within the Control Program environment, running concurrently with up to four mainframe sessions, but only one DOS session was supported at a time. This Control Program provided a rudimentary windowing interface accommodating up to seven windows: four dedicated to mainframe connections, one for a DOS session, and two notepad windows. These notepads facilitated transferring text from the DOS session into mainframe sessions; however, the reverse transfer was not possible. Due to the limited character display area, PC Magazine regarded the windowing capabilities as somewhat restricted and found the notepad functionality to have limited practical use. Additionally, the Control Program was noted for its high memory consumption, using roughly 200 KB of RAM. More impactful were specialized PC DOS utilities designed for file transfers between the PC and mainframes, including tools that supported ASCII to EBCDIC conversions and vice versa. At the time of introduction, the Control Program was priced around , while the file transfer utilities cost approximately . The availability of the Control Program was a key factor distinguishing the 3270 PC from an XT system equipped merely with an added 3278 interface card.
IBM categorized the 3270 PC Control Program as software intended for mainframe environments, which meant that any upgrades had to be installed by skilled system programmers rather than through user-initiated updates.
The PC/G and PC/GX variants featured an enhanced graphics-enabled version known as the Graphics Control Program (GCP). On the mainframe side, IBM’s Graphical Data Display Manager (GDDM), starting with release 4, offered support for these workstations, allowing users to perform local panning and zooming operations without imposing additional processing demands on the host mainframe.
In 1987, IBM launched the IBM 3270 Workstation Program, extending support to XT and AT models of 3270 PCs as well as standard XT/AT machines equipped with a 3278 board. This program enabled up to six simultaneous DOS 3.3 sessions while maintaining four active mainframe sessions along with two notepad windows.
Reception
In 1984, BYTE magazine commended the 3270 PC for its effective emulation of the 3278 terminal and its color display capabilities, ultimately recommending it as essential equipment for users requiring superior graphics or reliable mainframe connectivity.