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
3270 PC (System Unit 5271) - original 3270 PC, initially offered in three different Models numbered 2, 4, and 6. Model 2 has non-expandable memory of 256 KB and a single floppy drive. Model 4 has expandable memory, a second floppy drive, and a parallel port. Model 6 replaces one of the floppy drives with a 10 MB hard disk. Model 6 had a retail price of at its launch (with 512KB RAM), not including display, cables and software; a working configuration with an additional 192KB RAM, color display (model 5272) and the basic cabling and software (but without support for host/mainframe-side graphics) ran to . A 1985 review by PC Magazine found that fast file transfer to and from the mainframe was the strong selling point of this unit: file transfers that took hours with an Irma board took only minutes with the boards (and software) that came with the 3270 PC. The 3270 PC suffered however from incompatibility problems with other XT hardware and DOS software (for example, Microsoft QuickBasic). Its 3278 mainframe board was also considered lackluster, in comparison with an IBM 3279 graphics terminal, because it provides only a 24-line display during mainframe sessions, requiring either PC-side scrolling for the 32-line applications typically used with a 3279, or explicit 24-line application support on the mainframe side. later released Models 24 (two floppy drives) and 26 (floppy plus 10 MB hard-disk) supported and were bundled with the IBM 3295 Plasma Monitor. This monochrome display is intended to provide a high-capacity text terminal for simultaneous mainframe sessions. It has two sets of fonts: one with 612-pixel characters, with which it can display text in 62 rows by 160 columns, and a larger font with 916-pixel characters, with which it can display 46 rows by 106 columns of text. Models 30, 50, and 70 have 640 KB RAM on the system board, and follow same disk pattern as the initial models (one floppy, two floppies, and floppy plus hard drive) but with a 20 MB hard disk. They (and all subsequent models) also revert to the 5151/5272 Display Adapter (no Plasma Monitor support). Models 31, 51, and 71 revert to 256 KB RAM on the system board but were also shipped with an Expanded Memory Adapter (XMA) with 1 MB RAM standard. Optionally these models (released in 1986) could be equipped with up to 2 MB of XMA. Models P30/P50/P70 and P31/P51/P71 were like Models 30/50/70 and respectively 31/51/71 but with a 101-key (AT-style) keyboard replacing the 5271 Keyboard.
Models 31/51/71 and all P-models, require version 3.0 of the Control Program.