IBM 3270 AT
| Company type | Personal computer |
|---|---|
| Industry | Computer hardware |
| Founded | October 1983 |
| Products | Personal computers (3270 PC, 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, is an IBM personal computer that integrates standard PC XT components with specialized hardware and software to simulate an IBM 3270 terminal. This design enables it to function both as an independent PC and as a terminal connected to a mainframe system.
Subsequently, IBM released the 3270 AT (System Unit 5273), which is based on the IBM PC AT platform. Alongside this, advanced graphics models were made available for both XT and AT versions: the XT-derived 3270 PC/G and PC/GX (System Unit 5371) and their AT equivalents, the PC AT/G and PC AT/GX (System Unit 5373).
Technology
Most of the expansion slots in the system 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 at a resolution of 720×350 pixels, which can be viewed on either a color monitor (model 5272) or a monochrome display.
A specialized expansion card translates scancodes from the robust 122-key 5271 Keyboard into signals compatible with the XT architecture. Another essential card acts as a 3278 emulator, facilitating communication with the connected mainframe host.
Models
- 3270 PC (System Unit 5271) – Initially available in Models 2, 4, and 6:
- Model 2: featured fixed memory of 256 KB with no expansion options and included a single floppy drive.
- Model 4: offered expandable memory capacity, two floppy drives, and a parallel port.
- Model 6: replaced one floppy drive with a 10 MB hard disk; launched at approximately (512KB RAM), excluding cost for display and software; fully equipped setups could reach around .
A review in PC Magazine emphasized the system’s rapid mainframe file transfer capabilities but pointed out compatibility limitations with other XT hardware and DOS applications such as Microsoft QuickBasic. The mainframe interface board supported only a limited display of 24 lines, which was less than standard for graphic terminals.
Subsequent offerings included:
- Models 24 and 26, which came bundled with the IBM 3295 Plasma Monitor capable of displaying extensive text up to 62 rows by 160 columns.
- Models 30, 50, and 70 increased system RAM to 640 KB and incorporated larger hard drives of 20 MB while reverting to standard display adapters without Plasma Monitor support.
- Models 31, 51, and 71 reduced base RAM to 256 KB but included a standard Expanded Memory Adapter (XMA) with an option to expand up to 2 MB.
- P-series models (P30/P50/P70 and P31/P51/P71) mirrored these configurations but featured an updated 101-key AT-style keyboard.
Models released mid-decade required Control Program version 3.0.
- 3270 PC/G – A graphics-enhanced model utilizing APA graphics through an IBM 5278 Display Attachment Unit card that supports a resolution of 720×512 pixels along with CGA emulation; commonly paired with an IBM 5279 Color Display. Initial pricing started near . Available in Models12,14,16 offering improved memory options, a standard parallel port, and optional mouse support.
- 3270 PC/GX – Provided expanded APA graphics capabilities up to a resolution of 1024×1024 via IBM’s Display Attachment Unit; equipped with a larger 19-inch color or monochrome monitor (IBM5379). Pricing at launch was close to , increasing to nearly when bundled with required software and cables.
Upgrading from the base model to G or GX versions was not possible because these variants used different system units sold separately.
Later models based on the AT platform replicated these configurations:
- 3270 AT (System Unit5273), essentially the original design adapted to IBM AT hardware.
- 3270 AT/G and AT/GX (System Unit5373), corresponding respectively to the PC/G and PC/GX models but built on the AT architecture.
Software
When initially released, the 3270 PC utilized the 3270 PC Control Program as its operating environment, with PC DOS version 2.0 (upgraded later to 2.1) functioning as a subordinate task. This setup allowed only one PC DOS session to operate simultaneously alongside up to four mainframe connections. The Control Program incorporated a rudimentary windowing system capable of managing seven windows: four dedicated to mainframe sessions, one for DOS, and two notepads designed to facilitate text copying from DOS to mainframe sessions, though not in the reverse direction. Given the limited screen size, PC Magazine considered these windowing capabilities and notepad features to offer minimal practical benefit. Additionally, the Control Program was criticized for its heavy memory usage, occupying roughly 200 KB of RAM. More useful were the PC DOS file transfer tools (and ), which enabled exchanging files with the mainframe and converting between ASCII and EBCDIC formats. The pricing for the Control Program and these file transfer utilities was approximately and , respectively. At its debut, the Control Program set the 3270 PC apart from an XT equipped with a 3278 adapter.
IBM categorized the 3270 PC Control Program as software intended for mainframe environments; consequently, updates required intervention by specialized system programmers rather than being user-installable.
The PC/G and PC/GX variants employed an enhanced version known as the Graphics Control Program (GCP), which supported graphics capabilities. IBM's mainframe Graphical Data Display Manager (GDDM) starting from release 4 provided compatibility with these models, offering local pan and zoom functions that did not impose additional processing demands on the host mainframe.
In 1987, IBM launched the IBM 3270 Workstation Program compatible with both XT and AT versions of the 3270 PCs as well as standard XT and AT PCs fitted with a 3278 board. This software permitted up to six simultaneous DOS 3.3 sessions while continuing to support four mainframe connections and two notepad windows.
Reception
In 1984, BYTE commended the 3270 PC for its accurate 3278 emulation and vibrant color display, summarizing that it was an essential system for users requiring advanced graphics or robust mainframe communication capabilities.