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IBM 3270 PC/G

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IBM 3270 PC/G
IBM 3270 PC/G — XT-derived graphics-terminal workstation (machine type 5371) announced July 1984 (representative image of related 3270 PC family unit)
Specifications
DeveloperIBM Entry Systems Division, Boca Raton, in cooperation with IBM 3270 / GDDM groups
ManufacturerIBM
TypeMainframe graphics-terminal-emulation workstation
ReleasedJuly 1984
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
Storage5.25" 360 KB DSDD floppy (1 or 2) + optional hard disk
DisplayIBM 5278 Display Attachment Unit (external converter box) driving IBM 5279 Color Display (14"). Resolution: 720 × 512 APA (colour) plus CGA-compatible 320 × 200 / 640 × 200 modes
SoundPC speaker
OS / Firmware3270 PC Graphics Control Program (GCP) + PC DOS — a mainframe-graphics-aware variant of the 3270 PC Control Program, with local pan / zoom support for GDDM-generated images
PredecessorIBM 3270 PC (5271 — text-only mainframe-terminal version)
SuccessorIBM 3270 Workstation Program with graphics-capable adapter (1987+); IBM 6090 Graphics System for high-end CAD/CAM workloads
Model no.5371 — same system unit machine type as the IBM 3270 PC/GX (not 5372). The /G is differentiated from the /GX by its 5278 / 5279 display pair (vs the /GX's 5378 / 5379)

The IBM 3270 PC/G is the graphics-terminal-emulation variant of the IBM 3270 PC family, announced by IBM in July 1984. The "G" suffix designates Graphics — the /G provides high-resolution vector graphics support for IBM's GDDM (Graphical Data Display Manager) release 4+ mainframe graphics applications, with local pan and zoom that does not require a round-trip to the host mainframe.[1][2]

Important Machine-Type Note

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The 3270 PC/G uses system unit 5371. This is the same machine type as the IBM 3270 PC/GX — there is no "5372" 3270 PC product. The /G and /GX differ by their attached display hardware:

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

The 5371 system unit is a different machine type from the 5271 base 3270 PC, and a basic 5271 cannot be upgraded to a /G or /GX.

Launch and Pricing

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  • Announced July 1984 alongside the /GX.
  • Reference document: IBM GA33-3141-0 Introducing the IBM 3270 Personal Computer/G and /GX Workstations (May 1984).
  • Launch price: $11,240 retail for a working PC/G configuration with display.[3]
  • Model 16 (system unit alone, without graphics) was $6,580.
  • Discontinued 1987 alongside the rest of the 3270 PC line, after IBM released the 3270 Workstation Program software for standard PCs and PS/2s.

Models

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

Model 12 has a parallel port and the IBM 5277 mouse as standard — the higher-end models add the mouse as well but were originally shipped without it.

Hardware

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The 5371 system unit is a different machine type from the 5271 (3270 PC) but uses the same overall card-set approach. Specific to the PC/G:

  • IBM 5278 Display Attachment Unit — separate external box "packed with circuitry" — drives the 5279 monitor via a 75-pin connector. The 5278 carries the active vector-graphics hardware.
  • IBM 5279 Color Display — 14" colour CRT paired with the 5278 attachment box.
  • IBM 5277 mouse — 3-button, $340 standalone.
  • All other 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

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  • 720 × 512 APA in colour — the defining 3270 PC/G capability.
  • CGA-compatible 320 × 200 / 640 × 200 modes for DOS software.
  • Full-screen colour-mapped graphics suitable for mainframe-generated GDDM plots, CAD-style line drawings, and business charts.

Operating Environment: Graphics Control Program (GCP)

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The 3270 PC/G runs the Graphics Control Program (GCP) — a mainframe-graphics-aware variant of the standard 3270 PC Control Program. GCP adds:

  • Support for GDDM release 4+ mainframe graphics protocols.
  • Local pan / zoom of graphics images — manipulation happens in the 5278's local memory without round-tripping every operation back to the mainframe.
  • Mouse support via the IBM 5277.
  • Multi-session windowing (up to 4 mainframe sessions + 1 DOS task + 2 notepads), the same as the standard 3270 PC.

GDDM release 4 (and later releases) on the mainframe must be configured to talk to the /G workstation.[4]

Relationship to the IBM 3179G Terminal

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The 3270 PC/G is sometimes informally described as a workstation equivalent of the dedicated IBM 3179G Color Graphics Display Station. In fact the two products are contemporary — the 3179G was announced on 18 June 1985, after the PC/G's July 1984 launch. The PC/G is therefore not a "replacement" for the 3179G; rather, they are sibling products serving similar use cases via different chassis (PC/G = workstation with local DOS; 3179G = dedicated terminal with no local computing).

Common Faults

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The PC/G inherits all of the chassis-level faults of the IBM 3270 PC (RIFA mains-suppression caps in the PSU; tantalum bypass shorts on the planar; ageing 130 W IBM XT PSU). PC/G-specific faults:

  • IBM 5278 Display Attachment Unit — separate enclosure with its own PSU and active vector-graphics circuitry. This is the rarest single component in the PC/G system after 40+ years and is the most likely failure point. The 5278 is not interchangeable between PC/G and PC/GX configurations (the /GX uses the larger 5378).
  • IBM 5279 14" colour CRT — dedicated tube and timings; failure means substituting an IBM 5151 monochrome display (losing all graphics modes) is the only practical recovery.
  • 75-pin cable between 5278 and 5279 — proprietary; can develop intermittent contact at the connectors.
  • GCP system diskettes are rare in 2024; image them immediately if you have a working installation.

Service Documents

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  • IBM GA33-3141-0 — Introducing the IBM 3270 Personal Computer/G and /GX Workstations (May 1984). Primary reference document.[5]
  • IBM SA38-0037-00 — Personal Computer Family Service Information Manual (July 1989), Chapter 10.
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References

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  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
  4. ↑ https://www.ibm.com/docs/en/gddm?topic=gddm-3270-pcg-3270-pcgx-workstations
  5. ↑ https://www.bitsavers.org/pdf/ibm/pc/3270/3270_PC/GA33-3141-0_Introducing_the_IBM_3270_Personal_Computer_G_and_GX_Workstations_198405.pdf
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