IBM 3270 PC

The IBM 3270 PC (IBM System Unit 5271), released in October 1983, is an IBM PC XT containing additional hardware that, in combination with software, can emulate the behaviour of an IBM 3270 terminal. It can 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 is 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 are called 3270 PC/G and 3270 PC/GX and they use a different System Unit 5371, while their AT counterparts (PC AT/G and PC AT/GX) have System Unit 5373.
Technology.
The additional hardware occupies nearly all the free expansion slots in the computer. It includes a video card which occupies 1-3 ISA slots (depending on what level of graphics support is required), and supports CGA and MDA video modes. The display resolution is 720×350, either on the matching 14-inch color monitor (model 5272) or in monochrome on an MDA monitor.
A further expansion card intercepts scancodes from the 122-key 3270 keyboard, translating them into XT scancodes which are then sent to the normal keyboard connector. This keyboard, officially called the 5271 Keyboard Element, weighs 9.3 pounds.
The final additional card (a 3278 emulator) provides the communication interface to the host mainframe.
Models.
Models 31/51/71 and all P-models, require version 3.0 of the Control Program.
The basic 3270 PC could not be upgraded to the PC/G or PC/GX. These two models use a different basic unit (System Unit 5371), itself priced at $6,580 (for Model 16) without graphics.
Later, AT-based models:
Software.
At its launch, the 3270 PC used the 3270 PC Control Program as its operating system. PC DOS 2.0 (and later 2.1) can run as a task under the Control Program. Only one PC DOS task can be run at any given time, but in parallel with this, the Control Program can run up to four mainframe sessions. The Control Program also provides a basic windowing environment, with up to seven windows; besides the four mainframe and one DOS session, it also provides two notepads. The notepads can 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. More useful were the specialized PC DOS file transfer utilities that were available (called simply and ), which allow files to be exchanged with the mainframe and provide ASCII/EBCDIC conversion. The list prices for the Control Program and file transfer utilities were $300 and $600, respectively. 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.
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.
The PC/G and PC/GX models run 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) is 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.
In 1987 IBM released the IBM 3270 Workstation Program, which supports 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 allows up to six concurrent DOS 3.3 sessions, but the number of mainframe sessions and notepads remained the same (four and two, respectively).
Reception.
"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.