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IBM 3270 PC/GX

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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) via a larger external Display Attachment Unit driving a 19" IBM 5379 monitor.[1][2]

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 / 512 / 576 KB depending on submodel (12 / 14 / 16)
Storage5.25" 360 KB DSDD floppy (1 or 2) + optional hard disk
DisplayIBM 5378 Display Attachment Unit (external converter box, larger than the /G's 5278) driving IBM 5379 Color Display (19", available as 5379-C01 colour or 5379-M01 monochrome). Resolution: 1024 × 1024 APA
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

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: $18,490 (system + display), ~$20,000 for a working configuration with software and cables.[3] The /GX is roughly 65% more expensive than the /G — the premium pays for the 1024 × 1024 vector graphics capability and the 19" monitor.
  • Discontinued 1987 alongside the rest of the 3270 PC line.

Models

Same model numbering as the IBM 3270 PC/G:

IBM 3270 PC/GX (5371) submodels
Submodel Storage RAM
12 1 × floppy 384 KB
14 2 × floppy 512 KB
16 floppy + HDD 576 KB

Hardware

The 5371 system unit is identical between PC/G and PC/GX. The PC/GX-specific hardware is all in the external display subsystem:

  • IBM 5378 Display Attachment Unit — larger and more capable than the /G's 5278. Drives the 5379 19" monitor at 1024 × 1024 with full-screen vector graphics.
  • IBM 5379 Color Display — 19" colour CRT. Two variants:
5379-C01 — colour.
5379-M01 — monochrome.
  • IBM 5277 mouse — same 3-button mouse as the /G.
  • All system-unit cards (Keyboard Adapter, 3270 PC Display Adapter, APA, PSS, 3278/79 Emulation Adapter) are the same as the standard IBM 3270 PC.

Resolution and Graphics

  • 1024 × 1024 APA (Extended All Points Addressable) — the defining 3270 PC/GX capability.
  • CGA-compatible 320 × 200 / 640 × 200 modes for DOS software (downscaled / windowed to the 19" 5379).
  • 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 — Graphics Control Program (GCP) with multi-session windowing, GDDM release 4+ support on the mainframe, local pan / zoom that does not require host round-trip, mouse input via IBM 5277.

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 caps; tantalum bypass shorts; ageing 130 W IBM XT PSU). /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" CRT — premium 19" tubes are scarce and command high prices when available. A failed 5379 effectively retires the PC/GX from operation unless a donor 5379 can be sourced.
  • 75-pin cable between 5378 and 5379 — proprietary IBM; verify pinout against GA33-3141-0 if you must replace it.
  • GCP system diskettes — image immediately if you have an original set.

Service Documents

  • IBM GA33-3141-0 — Introducing the IBM 3270 Personal Computer/G and /GX Workstations (May 1984). Primary reference.
  • IBM SA38-0037-00 — Personal Computer Family Service Information Manual (July 1989), Chapter 10. Covers /GX as well as the standard 3270 PC and /G.

References


  1. ↑ IBM GA33-3141-0, Introducing the IBM 3270 Personal Computer/G and /GX Workstations, May 1984.
  2. ↑ https://en.wikipedia.org/wiki/IBM_3270_PC
  3. ↑ https://en.wikipedia.org/wiki/IBM_3270_PC
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