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IBM 3270 PC/GX

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Revision as of 22:03, 24 September 2026 by Josh (talk | contribs) (Fix refs so they render; the 5379 is powered FROM the 5378, not from its own socket; remove the phantom 75-pin cable (62-way bus extender to the system unit, 2 m cables to the display); add IBMs own 5378 internals (Motorola 68000, 128 KB shared memory, +5/-5/+12/-12 V supply, eight logic cards incl up to three bit-plane cards) and the full 5379 specification; Model 016 is 576 KB on a /GX)
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IBM 3270 PC/GX
IBM 3270 PC/GX — XT-derived extended-graphics workstation (system unit 5371) with 1024 × 1024 APA and IBM 5379 19" display
Specifications
DeveloperIBM Entry Systems Division, Boca Raton, in cooperation with IBM 3270 / GDDM groups
ManufacturerIBM
TypeHigh-resolution mainframe graphics workstation
ReleasedJuly 1984 (announced alongside the 3270 PC/G)
Discontinued1987 (alongside the rest of the 3270 PC line)
CPUIntel 8088 @ 4.77 MHz — same chassis as IBM 3270 PC
Memory384 KB (Model 012), 512 KB (014) or 576 KB (016). The /GX ceiling is 576 KB, not the /G's 640 KB
StorageOne or two dual-sided 5.25-inch diskette drives; a 10 MB fixed disk on Model 016
DisplayIBM 5378 Display Attachment Unit — a Motorola 68000 graphics engine with 128 KB of its own memory — driving the IBM 5379 19-inch display, Model C01 colour or M01 monochrome. 1024 × 1024 pels in the graphics layer, 52 frames per second non-interlaced
SoundPC speaker
OS / Firmware3270 PC Graphics Control Program (GCP) + PC DOS — same as the IBM 3270 PC/G but driving the larger display and higher resolution
PredecessorIBM 3270 PC (5271 — text-only) and IBM 3270 PC/G (smaller-display sibling)
SuccessorIBM 3270 Workstation Program (1987) on standard PCs with appropriate graphics; IBM 6090 Graphics System for CAD/CAM
Model no.5371 — same system unit as the IBM 3270 PC/G (not 5372). The /GX is differentiated from the /G by its 5378 attachment unit and 5379 19" display

The IBM 3270 PC/GX is the extended-graphics ("GX") variant of the IBM 3270 PC family, announced by IBM in July 1984 alongside the standard graphics PC/G. The "GX" suffix designates Graphics eXtended — the /GX provides 1024 × 1024 APA resolution (significantly higher than the /G's 720 × 512) through a display attachment unit built around a Motorola 68000, driving a 19-inch IBM 5379 display.[1][2]

Important Machine-Type Note

The 3270 PC/GX uses system unit 5371 — the same machine type as the IBM 3270 PC/G. There is no separate "5372" for the GX in any IBM source the wiki has located. The /G and /GX are differentiated by their attached display hardware:

  • IBM 3270 PC/G: IBM 5278 Display Attachment Unit + IBM 5279 14" Color Display, 720 × 512 APA.
  • 3270 PC/GX (this page): IBM 5378 Display Attachment Unit + IBM 5379 19" Color Display, 1024 × 1024 APA.

The AT-based equivalent (PC AT/G and AT/GX) uses system unit 5373, not 5371.

Launch and Pricing

  • Announced July 1984 alongside the /G.
  • Reference document: IBM GA33-3141-0 Introducing the IBM 3270 Personal Computer/G and /GX Workstations (May 1984).
  • Launch price: about $18,490 for system and display, and about $20,000 for a working configuration with software and cables — roughly 65 per cent more than a /G.[3]
  • Discontinued 1987 alongside the rest of the 3270 PC line.

Models

The 5371 models carry the same numbers as the /G's but not the same memory:[2]

IBM 3270 PC/GX — 5371 models
Model RAM Storage Standard adapters
012 384 KB, expandable to 576 KB One dual-sided diskette drive Diskette Adapter, 3270 System Adapter, Display Unit Adapter, Keyboard/Tablet/Mouse Adapter, Printer Adapter
014 512 KB (012 plus 128 KB), expandable to 576 KB Second dual-sided diskette drive As 012
016 576 KB (012 plus 192 KB) 10 MB fixed disk plus its adapter card As 012

Model 016 is 576 KB on a /GX and 640 KB on a /G — same machine type, different memory ceiling, because the /GX's display subsystem takes more of the address space.[2]

Special features are the same list as the /G except that IBM names the 5152 Monochrome Printer rather than the Graphics Printer: 5277 Mouse, 5083 Tablet Model 002 with cursor or stylus, 5152 printer, 3852 Model 001 Color Ink Jet Printer, IEEE-488 Adapter, RS232C Adapter, APL Keyboard, and the PC Bus Extension Adapter on Models 012 and 014 only.[2]

Hardware

The 5371 system unit is the same as the /G's. Everything that makes a /GX is in the display subsystem.

IBM 5378 Display Attachment Unit

The 5378 is not a bigger 5278 — it is a different machine. IBM's description:[2][4]

  • A Motorola 68000 graphics processor performing vector, character and image processing. This is what gives the /GX its performance advantage over the /G.
  • 128 KB of memory for vector lists, standard and user-defined characters, character buffers and system functions, shared between the 68000 and the system unit's 8088 or 80286.
  • Connected to the system unit by a 62-way bus extender cable — 1 m (3.3 ft) — and to the 5379 by 2 m (6.6 ft) cables.
  • Its own power supply producing +5 V, −5 V, +12 V and −12 V, and a logic gate holding up to eight four-wide by three-high logic cards: display bus receiver, graphics processor, system control, update control, clock and video driver, and up to three bit-plane cards.
  • Model C01 supports the 5379 Color Display; Model M01 supports the 5379 Monochrome Display. They are not interchangeable.
  • 495 mm wide × 406 mm deep × 130 mm high; 14 kg (31 lb). It can be stacked above or below the 5371, 5373 or 5161.
  • It has a 1.8 m (6 ft) power cable and requires its own power source.

The 5379 display is powered from the 5378, not from the wall and not from the system unit. IBM's own set-up instruction says so in as many words: "Ensure that the power cable of the 5379 display is plugged into the 5378 DAU and NOT into the system unit."[4] There are two mains-fed units in a /GX — the system unit and the 5378 — not three.

IBM's own hazard labels tell you what is inside each box. The safety inspection parts list for these machines specifies a "Label — Hazard, 25000 V" and a "Label — Hazard, 800 V".[4] The 25 kV label is the display's anode. The 800 V label is on the display attachment unit — which is worth pausing on, because the 5378 looks like a logic box and is usually described as one. Treat it as a mains-powered device with a high-voltage section, not as a peripheral.

IBM 5379 Display

IBM's specification:[2]

  • 19 inches diagonal, viewing area 280 × 280 mm (11 × 11 in).
  • 50 rows of 80 characters (4,000) in the alphameric layer.
  • 1024 × 1024 pels in the graphics layer, 93 pels per inch — IBM notes this equals the resolution of the 5080 Graphics System Display. Graphics Control Program Version 1 supports 960 × 1000 in a 261 × 279 mm area.
  • 52 frames per second, non-interlaced.
  • Colour model: up to 16 colours in the graphics layer and eight in the alphameric layer. Monochrome: four intensities graphics, two alphameric.
  • Characters in a 12 × 20 box.
  • Brightness control on both; degauss control on the colour display.
  • 100 to 127 V, 50 or 60 Hz.
  • 500 mm wide; 488 mm deep (colour) or 525 mm (monochrome); 460 mm high. 35 kg (77 lb). Tilt −5 to +15°, swivel ±120°.

At 35 kg this is a two-person lift, and the swivel range means it will happily rotate itself off a desk edge.

Resolution and Graphics

  • 1024 × 1024 pels in the graphics layer — the defining 3270 PC/GX capability.
  • Sufficient resolution for sustained CAD-style line drawings, mainframe-generated GDDM plots at multi-megapixel detail, and engineering documentation reading.

Operating Environment

Same as the IBM 3270 PC/G — the Graphics Control Program with multi-session windowing, and GDDM on the host. IBM notes that GDDM Release 4 adds 5379-specific functions including three-dimensional support, 16 colours, and offloading vector conversion from the host to the workstation, which reduces the load the workstation places on the mainframe.[2][5]

The /GX's higher resolution means each mainframe session window can be larger than on the /G's 5279, and more of them can be visible simultaneously without overlap.

Common Faults

The /GX inherits all of the chassis-level faults of the IBM 3270 PC (RIFA mains-suppression capacitors; tantalum bypass shorts on the planar). /GX-specific faults are dominated by the rarity of the 5378 / 5379 pair:

  • IBM 5378 Display Attachment Unit — the rarest single component in the PC/GX system. Built specifically for high-resolution vector graphics; not interchangeable with the /G's 5278.
  • IBM 5379 19-inch CRT — scarce, heavy, and carrying IBM's 25000 V hazard label. A failed 5379 effectively retires the workstation unless a donor can be found, and the colour and monochrome models need matching C01 or M01 attachment units.
  • Error codes in the 44XX range indicate the display attachment unit and its display as a pair; IBM does not separate them in the FRU table.[2]
  • The cables — a 62-way bus extender from the system unit to the 5378, and 2 m cables from the 5378 to the 5379. All IBM-supplied proprietary assemblies.[4][2]
  • GCP system diskettes — image immediately if you have an original set.

Service Documents

References

  1. ↑ IBM, Introducing the IBM 3270 Personal Computer/G and /GX Workstations, GA33-3141-0, May 1984, at bitsavers.org/pdf/ibm/pc/3270/3270_PC/.
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 IBM, IBM Personal Computer Family Service Information Manual, SA38-0037-00, July 1989 — hosted on this wiki as IBM Personal Computer Family Service Information Manual. Chapter 10, "3270 PC Products", is the source for the system-unit and display combinations, the full 5271, 5371 and 5373 model lists, the 5371 and 5373 slot allocations, the unit specifications for the 5371, 5278, 5279, 5378 and 5379, the statement of which unit powers which, the 3270 unique error code to FRU indication table, the diagnostic tips and the ECA history. Chapter 18, "Personal Computer Parts Catalog", is the source for the 5271, 5371 and 5373 FRU part numbers and for IBM's note that "all base system parts for the 3270 XT products are the same as 5160 XT base system parts".
  3. ↑ Wikipedia, "IBM 3270 PC". Tertiary; used only for the launch and withdrawal chronology and the retail prices, which no IBM document located during verification confirms.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 IBM, IBM 3270 PC AT/G and AT/GX Maintenance Information, SY33-0125-1 — hosted on this wiki as IBM 3270 PC AT/G and AT/GX Maintenance Information. The safety inspection checklist and its parts list, which specify the "Label - Hazard, 25000 V" on the display and the "Label - Hazard, 800 V" on the display attachment unit; the chapter 1 description of the 5378 DAU (the 62-way bus extender cable to the system unit, the internal supply producing +5 V, −5 V, +12 V and −12 V, and the logic gate holding up to eight four-wide by three-high cards — display bus receiver, graphics processor, system control, update control, clock and video driver, and up to three bit-plane cards); and the diagnostic set-up instruction that the 5379's power cable must be plugged into the 5378 DAU and not into the system unit.
  5. ↑ IBM, GDDM documentation, "3270 PC/G and 3270 PC/GX workstations", at ibm.com/docs/en/gddm.


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