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Fix refs so they render; replace the invented model table with IBMs own (only Models 070/071 have the 20 MB disk; XMA is 1 MB not 2 MB; Models 024/026 use a Plasma Keyboard Adapter); the host link is COAX not twinax and is point-to-point with no terminator - IBMs test is <1 ohm at the connector; add the 3270 unique error-code to FRU table and the documented false 2801 and false 8505; state IBMs own note that all base system parts are 5160 XT parts
 
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| discontinued  = 1987 (superseded by IBM 3270 Workstation Program software running on standard PCs and PS/2s)
| discontinued  = 1987 (superseded by IBM 3270 Workstation Program software running on standard PCs and PS/2s)
| cpu          = Intel '''8088 @ 4.77 MHz''' — identical to the [[IBM PC XT (5160)|IBM PC XT]] planar
| cpu          = Intel '''8088 @ 4.77 MHz''' — identical to the [[IBM PC XT (5160)|IBM PC XT]] planar
| memory        = 256 KB minimum (Model 2 fixed); 512–640 KB on Models 4 / 6 / 24 / 26 / 30 / 50 / 70; up to 2 MB on 31 / 51 / 71 with the Expanded Memory Adapter (XMA)
| memory        = 256 KB on the system board on Models 002, 004, 006, 024, 026, 031, 051 and 071; '''640 KB''' on the system board on Models 030, 050 and 070. Models 004, 006, 024, 026 and 051 add a Printer/Memory Adapter carrying a further 128 KB; Models 031, 051 and 071 carry an '''Expanded Memory Adapter (XMA) with 1 MB'''
| storage      = 5.25" 360 KB DSDD floppy (1 or 2); optional 10 MB ST-412 hard drive (Model 6) or 20 MB hard drive (Models 30 / 50 / 70 from 1986)
| storage      = 5.25-inch 360 KB diskette drive (full-height on Models 002&ndash;026, half-high on Models 030 onwards), one or two. '''10 MB''' fixed disk on Models 006 and 026; '''20 MB''' on Models 070 and 071 only &mdash; Models 030 and 050 are diskette-only
| display      = '''IBM 5272 Color Display''' (14" tilt/swivel, 720×350, 7 colours, 24 kHz hsync), or '''IBM 5151''' monochrome, or '''IBM 3295 Plasma Monitor''' (Models 24/26)
| display      = '''IBM 5272 Color Display''' (14" tilt/swivel, 720×350, 7 colours, 24 kHz hsync), or '''IBM 5151''' monochrome, or '''IBM 3295 Plasma Monitor''' (Models 24/26)
| sound        = PC speaker
| sound        = PC speaker
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| predecessor  = [[IBM PC XT (5160)]] (chassis) and IBM 3278 / 3279 terminals (function)
| predecessor  = [[IBM PC XT (5160)]] (chassis) and IBM 3278 / 3279 terminals (function)
| successor    = IBM 3270 Workstation Program (1987) — same multi-session experience on a standard XT/AT with only a 3278/79 emulation card
| successor    = IBM 3270 Workstation Program (1987) — same multi-session experience on a standard XT/AT with only a 3278/79 emulation card
| model        = 5271 (system unit machine type). Submodels: 2, 4, 6, 24, 26, 30, 31, 50, 51, 70, 71, and P-prefix variants (P30, P31, P50, P51, P70, P71)
| model        = 5271 (system unit machine type). Submodels 002, 004, 006, 024, 026, 030, 031, 050, 051, 070, 071, and the P variants P30, P31, P50, P51, P70 and P71, which swap the 5271 keyboard for the 101-key Enhanced Keyboard and a Cable Adapter and require Control Program 3.0
}}
}}


The '''IBM 3270 PC''' (machine type '''5271''') is a mainframe-terminal-emulation workstation announced by IBM on '''18 October 1983''' (announcement letter '''183-129''').<ref>https://sharktastica.co.uk/resources/docs/IBM_183-129_3270PC_83.pdf</ref> The system unit is essentially an [[IBM PC XT (5160)]] motherboard, chassis, and PSU, but with the eight ISA expansion slots almost entirely occupied by specialist 3270-terminal-emulation cards. The combination of these cards plus the '''3270 PC Control Program''' allows the workstation to host '''up to four mainframe terminal sessions, one DOS task, and two notepads''' simultaneously in a windowed display — a unique capability in 1983.<ref>https://en.wikipedia.org/wiki/IBM_3270_PC</ref>
The '''IBM 3270 PC''' (machine type '''5271''') is a mainframe-terminal-emulation workstation announced by IBM on '''18 October 1983''' (announcement letter '''183-129''').<ref name="al183129">IBM Announcement Letter 183-129, 18 October 1983, mirrored at <code>sharktastica.co.uk/resources/docs/IBM_183-129_3270PC_83.pdf</code>.</ref> The system unit is an [[IBM PC XT (5160)]] with the expansion slots almost entirely occupied by specialist 3270 cards. IBM says so itself, in the parts catalogue: '''"all base system parts for the 3270 XT products are the same as 5160 XT base system parts"'''.<ref name="sim">IBM, ''IBM Personal Computer Family Service Information Manual'', SA38-0037-00, July 1989 &mdash; 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".</ref> That is the single most useful fact about servicing one &mdash; planar, power supply, drives, covers and keyboard cable are all XT parts, and only the 3270 cards and the displays are unique. The combination of these cards plus the '''3270 PC Control Program''' allows the workstation to host '''up to four mainframe terminal sessions, one DOS task, and two notepads''' simultaneously in a windowed display — a unique capability in 1983.<ref name="wp3270">Wikipedia, "IBM 3270 PC". Tertiary; used for the launch and withdrawal chronology and the retail prices.</ref>


The 3270 PC was '''discontinued in 1987''' when IBM released the '''3270 Workstation Program''' (a software-only product that ran on standard PCs/PS/2s with only a 3278/79 Emulation Adapter), removing the need for the 3270 PC's specialised cards.
The 3270 PC was '''discontinued in 1987''' when IBM released the '''3270 Workstation Program''' (a software-only product that ran on standard PCs/PS/2s with only a 3278/79 Emulation Adapter), removing the need for the 3270 PC's specialised cards.
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== Models ==
== Models ==


{| class="wikitable styled-table" style="width:70%; text-align:center;"
IBM's own model list, from chapter 10 of the Service Information Manual. Read it as a list of what is fitted rather than as a spec ladder &mdash; the memory is split between the system board and adapter cards in a way that catches people out.<ref name="sim" />
|+'''IBM 3270 PC (5271) submodels'''
 
! Submodel !! Storage !! RAM !! Notes
<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:100%;"
|+'''IBM 3270 PC (5271) models'''
! Model !! System board RAM !! Display adapter !! Diskette !! Fixed disk !! Other
|-
| '''002''' || 256 KB || 5151/5272 || 1 × 360 KB || &mdash; || 5271 Keyboard and Keyboard Adapter; 3270 Systems Adapter (DFCA)
|-
| '''004''' || 256 KB || 5151/5272 || 2 × 360 KB || &mdash; || Printer/Memory Adapter with 128 KB
|-
| '''006''' || 256 KB || 5151/5272 || 1 × 360 KB || 10 MB || Printer/Memory Adapter with 128 KB
|-
| '''024''' || 256 KB || '''3295 Plasma''' || 2 × 360 KB || &mdash; || '''Plasma Keyboard Adapter'''; Printer/Memory Adapter with 128 KB
|-
| '''026''' || 256 KB || '''3295 Plasma''' || 1 × 360 KB || 10 MB || '''Plasma Keyboard Adapter'''; Printer/Memory Adapter with 128 KB
|-
|-
| 2 || 1 × floppy || 256 KB fixed || Entry; not RAM-expandable
| '''030''' || '''640 KB''' || 5151/5272 || 1 × 360 KB half-high || &mdash; || Printer Adapter
|-
|-
| 4 || 2 × floppy || up to 640 KB ||
| '''050''' || '''640 KB''' || 5151/5272 || 2 × 360 KB half-high || &mdash; ||
|-
|-
| '''6''' || floppy + 10 MB HDD || up to 640 KB || Most common configuration
| '''070''' || '''640 KB''' || 5151/5272 || 1 × 360 KB half-high || '''20 MB''' ||
|-
|-
| 24 / 26 || 2 × floppy / floppy + HDD || up to 640 KB || Added 25 Oct 1984 (announcement 184-136); IBM 3295 Plasma Monitor support
| '''031''' || 256 KB || 5151/5272 || 1 × 360 KB half-high || &mdash; || '''XMA with 1 MB''' (includes Printer Adapter); needs Control Program 3.0
|-
|-
| 30 / 50 / 70 || various || 640 KB on planar, 20 MB HDD || Added 1986 (announcement 186-053)
| '''051''' || 256 KB || 5151/5272 || 2 × 360 KB half-high || &mdash; || XMA with 1 MB; Printer/Memory Adapter with 128 KB; Control Program 3.0
|-
|-
| 31 / 51 / 71 || various || 256 KB planar + 1 MB on Expanded Memory Adapter card || 1986 generation
| '''071''' || 256 KB || 5151/5272 || 1 × 360 KB half-high || '''20 MB''' || XMA with 1 MB; Control Program 3.0
|-
|-
| P30 / P31 / P50 / P51 / P70 / P71 || various || various || Use 101-key Enhanced AT-style keyboard instead of the 122-key
| '''P30, P31, P50, P51, P70, P71''' || colspan="5" | As the corresponding numeric model, except that an '''Enhanced (101-key) Keyboard and a Cable Adapter''' replace the 5271 Keyboard. All P models require Control Program 3.0.
|}
|}


The 1984 expansion announcement (184-136, 25 October 1984) added '''IBM 3295 Plasma Monitor''' support — an orange-plasma display capable of 62 × 160 or 46 × 106 text grids, far beyond the 5272's text capabilities.<ref>http://www-01.ibm.com/common/ssi/rep_ca/6/897/ENUS184-136/index.html</ref>
Three things in that table are commonly got wrong:


The 1986 expansion (186-053) added '''640 KB on the planar''' and the '''XMA Expanded Memory Adapter''' (up to 1 MB of EMS-style expansion memory) on the 31/51/71 submodels.<ref>http://www-01.ibm.com/common/ssi/printableversion.wss?docURL=/common/ssi/rep_ca/3/897/ENUS186-053/index.html</ref>
* '''Only Models 070 and 071 have the 20 MB fixed disk.''' Models 030 and 050 are diskette-only despite being in the same 1986 group.
* '''The XMA carries 1 MB, not 2 MB.'''
* '''Models 024 and 026 use a different keyboard adapter''' &mdash; IBM calls it the '''Plasma Keyboard Adapter''' &mdash; alongside the 3295 Plasma Display Adapter. A standard Keyboard Adapter is not a substitute.
 
IBM also records a documented trap for the XMA: '''jumpered as LPT2 on a 5271 with a fixed disk, the XMA is not supported''' &mdash; there is an interrupt-level conflict.<ref name="sim" />


== Launch Pricing ==
== Launch Pricing ==


* '''Model 6''' (512 KB + 10 MB HDD): '''$6,210 system unit only'''.
* '''Model 006''' (256 KB system board plus a 128 KB Printer/Memory Adapter, with the 10 MB fixed disk): '''$6,210''' for the system unit alone.<ref name="wp3270" />
* Typical working colour-monitor configuration: '''~$8,465''' including software and cabling.<ref>PC Magazine, 22 January 1985 — Valenzuela review.</ref>
* Typical working colour-monitor configuration: about '''$8,465''' including software and cabling.<ref name="pcmag85">''PC Magazine'', 22 January 1985, Valenzuela review of the 3270 PC. Also the source of the "memory hog" characterisation of the Control Program.</ref>


== Specialist Cards ==
== Specialist Cards ==
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:: '''Simple''' (ROM '''6323581''')
:: '''Simple''' (ROM '''6323581''')
:: '''Complicated''' (ROM '''6323582''') — adds NMI button and serial port.
:: '''Complicated''' (ROM '''6323582''') — adds NMI button and serial port.
* '''Critical: this card holds the video BIOS''' for the 3270 PC Display Adapter — the video cards do not work without the keyboard adapter card installed.<ref>http://www.seasip.info/VintagePC/5271.html</ref>
* '''Critical: this card holds the video BIOS''' for the 3270 PC Display Adapter — the video cards do not work without the keyboard adapter card installed.<ref name="seasip">John Elliott, [http://www.seasip.info/VintagePC/5271.html The IBM 5271 (aka 3270 PC)], seasip.info. A community technical reference built from a working machine: the card complement and what each card does, the video BIOS living in the keyboard controller ROM (part 6323581 for the "simple" controller and 6323582 for the "complicated" one), the error codes 3201, 3202, 3203 and 2801, the 5272 display timings, and the statement that the case, motherboard, drives and power supply are all identical or very similar to the XT.</ref>
* On Models 024 and 026, which drive the 3295 Plasma Monitor, IBM fits a '''Plasma Keyboard Adapter''' in place of the standard one.<ref name="sim" />


=== 3270 PC Display Adapter ===
=== 3270 PC Display Adapter ===
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=== 3278/79 Host Connect / Emulation Adapter ===
=== 3278/79 Host Connect / Emulation Adapter ===


* '''BNC twinax''' connection to the IBM '''3174''' or '''3274''' cluster controller.
* IBM calls this card the '''DFCA''' — Distributed Function Communications Adapter — and that is the name the diagnostics and the FRU tables use.<ref name="sim" /><ref name="mi3270">IBM, ''IBM 3270 Personal Computer Maintenance Information'', SY27-2567-2, third edition, October 1984 &mdash; hosted on this wiki as [[IBM 3270 PC Maintenance Information]]. The safety inspection checklist; the problem isolation charts, including the coaxial cable connection test and the coaxial cable resistance check; section 4, locations, including the system board diagram; section 5, removal, replacement and adjustments; and section 7, the illustrated parts catalogue for the 5271 system unit, the 5161 Expansion Unit, the 5151 Monochrome Display, the 5272 Color Display and the keyboard.</ref>
* '''Coaxial''' connection to an IBM '''3274''' (later 3174) control unit. '''It is coax, not twinax''' — twinax is the midrange 5250 attachment and will not work here — and the link is point to point, one control-unit port per workstation, with '''no terminator'''.<ref name="mi3270" /><ref name="sim" />
* Two variants exist:
* Two variants exist:
:: Older — 4 KB buffer, I/O at '''2D0h–2D6h'''.
:: Older — 4 KB buffer, I/O at '''2D0h–2D6h'''.
:: Newer — adds register at '''2D7h'''; reconfigurable buffer size.
:: Newer — adds register at '''2D7h'''; reconfigurable buffer size.
* Technical reference: '''IBM 1502336''' — ''PC 3278/79 Emulation Adapter Technical Reference'' (October 1983).<ref>http://bitsavers.trailing-edge.com/pdf/ibm/pc/cards/1502336_PC_3278_79_Emulation_Adapter_Technical_Adapter_Oct83.pdf</ref>
* Technical reference: '''IBM 1502336''' — ''PC 3278/79 Emulation Adapter Technical Reference'' (October 1983), at <code>bitsavers.org/pdf/ibm/pc/cards/</code>.


[[File:IBM 5271 physical layout.svg|center|thumb|480px|IBM 5271 (3270 PC) physical layout diagram showing slot placement for the keyboard adapter, display adapter, host-connect card, and the optional APA / PSS expansion cards. (Image: Wikimedia Commons, public domain)]]
[[File:IBM 5271 physical layout.svg|center|thumb|480px|IBM 5271 (3270 PC) physical layout diagram showing slot placement for the keyboard adapter, display adapter, host-connect card, and the optional APA / PSS expansion cards. (Image: Wikimedia Commons, public domain)]]
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'''Control Program v3.0''' is required for the 1986 Models 31/51/71 and all P-models.
'''Control Program v3.0''' is required for the 1986 Models 31/51/71 and all P-models.


In '''1987''' the '''3270 Workstation Program''' (IBM '''84X0982''') replaced the Control Program, providing the same multi-session experience on a standard XT or AT with only a 3278/79 Emulation Adapter — and adding DOS 3.3 support plus up to six DOS sessions.<ref>http://www.bitsavers.org/pdf/ibm/pc/3270/84X0982_3270_Workstation_Program_V1.0_Users_Guide_and_Reference_Apr87.pdf</ref>
In '''1987''' the '''3270 Workstation Program''' (IBM '''84X0982''') replaced the Control Program, providing the same multi-session experience on a standard XT or AT with only a 3278/79 Emulation Adapter — and adding DOS 3.3 support plus up to six DOS sessions.<ref name="wsp87">IBM, ''3270 Workstation Program Version 1.0 User's Guide and Reference'', 84X0982, April 1987, at <code>bitsavers.org/pdf/ibm/pc/3270/</code>.</ref>


=== File Transfer ===
=== File Transfer ===
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== Display ==
== Display ==


* '''IBM 5272 Color Display''' — 14" tilt/swivel, '''720 × 350''' in '''7 colours''' (no high-intensity; bright and standard CGA colours render identically). Pin 4 of the DE-9 selects mono vs colour. Color timings: '''hsync 24 kHz negative, vsync 63 Hz negative'''. Mono timings: 18.6 kHz / 50 Hz.<ref>http://www.seasip.info/VintagePC/5271.html</ref>
* '''IBM 5272 Color Display''' — 14" tilt/swivel, '''720 × 350''' in '''7 colours''' (no high-intensity; bright and standard CGA colours render identically). Pin 4 of the DE-9 selects mono vs colour. Color timings: '''hsync 24 kHz negative, vsync 63 Hz negative'''. Mono timings: 18.6 kHz / 50 Hz.<ref name="seasip" />
* '''IBM 5151''' monochrome — also supported (the graphics card auto-detects monitor type via pin 4).
* '''IBM 5151''' monochrome — also supported (the graphics card auto-detects monitor type via pin 4).
* '''IBM 3295 Plasma Monitor''' — orange plasma, '''62 × 160''' or '''46 × 106''' text grids, supported on Models 24/26.
* '''IBM 3295 Plasma Monitor''' — orange plasma, '''62 × 160''' or '''46 × 106''' text grids, supported on Models 24/26.
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* '''Weight: 9.3 lb''' (much heavier than a standard PC keyboard).
* '''Weight: 9.3 lb''' (much heavier than a standard PC keyboard).
* '''AT protocol''', scan code set 3.
* '''AT protocol''', scan code set 3.
* First announced October 1983; shipped Q1 1984.<ref>https://sharktastica.co.uk/wiki/ibm-model-f</ref><ref>https://deskthority.net/wiki/IBM_Model_F_122-key</ref>
* First announced October 1983; shipped Q1 1984.<ref name="kbwiki">[https://sharktastica.co.uk/wiki/ibm-model-f sharktastica.co.uk &mdash; IBM Model F] and [https://deskthority.net/wiki/IBM_Model_F_122-key deskthority &mdash; IBM Model F 122-key]. Community keyboard references; the source for the 9.3 lb weight and the scan-code-set-3 behaviour. </ref> IBM's own parts catalogue lists keyboard part '''6110344''' for the 5271 in Figure 7 of the maintenance manual.<ref name="mi3270" />


The keyboard connects to the '''keyboard adapter dongle''' — a small cable that splits a DE-9 on the keyboard controller card into two 5-pin DIN connectors (one for the 3270 keyboard, one passing through to the planar XT keyboard socket).
The keyboard connects to the '''keyboard adapter dongle''' — a small cable that splits a DE-9 on the keyboard controller card into two 5-pin DIN connectors (one for the 3270 keyboard, one passing through to the planar XT keyboard socket).
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[[File:IBM Model F 122 key keyboard.jpg|center|thumb|480px|The IBM 122-key Model F keyboard (IBM part 6110344) — the 5271 Keyboard Element used on all 3270 PC family machines. (Image: Wikimedia Commons, CC BY-SA 4.0)]]
[[File:IBM Model F 122 key keyboard.jpg|center|thumb|480px|The IBM 122-key Model F keyboard (IBM part 6110344) — the 5271 Keyboard Element used on all 3270 PC family machines. (Image: Wikimedia Commons, CC BY-SA 4.0)]]
== What IBM's Error Codes Point At ==
The 3270 PC posts error codes in ranges that a plain XT does not use, and IBM publishes the mapping from code range to field-replaceable unit:<ref name="sim" />
{| class="wikitable styled-table" style="width:85%;"
|+'''3270 unique error codes and the FRU each range indicates'''
! Code range !! FRU indicated
|-
| '''28XX''' || DFCA card (the 3278/79 Emulation Adapter)
|-
| '''32XX''' || Display Adapter card, Programmed Symbols Adapter card, All-Points-Addressable Adapter card, Extended Graphics Adapter card (3270 PC AT only), or the Top Card Connector
|-
| '''44XX''' || Display Attachment Unit — the 5278 with its 5279, or the 5378 with its 5379 (3270 PC/G and /GX)
|-
| '''45XX''' || IEEE Interface Adapter card (IEEE-488)
|}
Two documented traps in that table:
* '''A 2801 can be false.''' If a long DFCA has been replaced with the newer short adapter card, the Keyboard Timer Adapter may also need changing. If you get a 2801, press F1 to continue after POST, and the host session then establishes normally, the 2801 is false. IBM's '''ECA001''' directs the engineer to order '''P/N 1497249''' (one EPROM) and replace the pluggable EPROM on the Keyboard Timer Adapter.<ref name="sim" />
* '''The XMA can post a false 8505.''' The diagnostic for the XMA (P/N 4466857 with piggy-back memory P/N 4466858) tests the D000&ndash;DFFF address range; any other adapter with RAM or ROS in that range produces a false 8505.<ref name="sim" />
The coaxial link has its own isolation chart in the maintenance manual, and it ends in a measurement worth knowing: with the machine powered off and the cable disconnected, '''the resistance at the system unit's coax connector should be less than 1 ohm'''. If it is not, IBM's instruction is to replace the DFCA.<ref name="mi3270" /> IBM also warns, twice, '''not to connect or disconnect the coaxial cable during an electrical storm''' — the cable run to the control unit can be long and is often between buildings.<ref name="mi3270" />


== Common Faults ==
== Common Faults ==


The 3270 PC chassis is identical to a stock IBM PC XT, so chassis faults are:
The chassis is a stock IBM PC XT — IBM says so in its own parts catalogue<ref name="sim" /> — so chassis faults are XT faults:


* '''RIFA-branded X / Y mains-suppression caps''' in the PSU — vent and produce smoke / fish odour. Replace immediately.
* '''RIFA-branded X / Y mains-suppression caps''' in the PSU — vent and produce smoke / fish odour. Replace immediately.
* '''Tantalum bypass cap shorts''' on the planar — pull the +5 V rail.
* '''Tantalum bypass capacitor shorts''' on the planar — these pull the +5 V rail down. The 5160 board carries sixteen tantalums, thirteen of them on +5 V, and they fail at or shortly after power-on.<ref name="mz">[https://www.minuszerodegrees.net/failure/failure.htm Commonly Failing Electronic Components (in vintage computers)] and [https://www.minuszerodegrees.net/5150_5160/MDC/tantalum_short_plus_5volts.htm Short-circuit on the +5 volt line of an IBM 5150/5155/5160 motherboard], minuszerodegrees.net. Sources for the tantalum failure modes on 51xx boards and for the count of sixteen tantalums on the 5160 motherboard, thirteen of them on the +5 V line. Community sources that mirror IBM data; they apply to the 3270 PC because IBM states the base system parts are the same as the 5160 XT's.</ref>
* '''Hard disk failure''' on Model 6 / 30 / 50 / 70 — original ST-412 / ST-225 drives are end-of-life.
* '''Hard disk failure''' on Model 6 / 30 / 50 / 70 — original ST-412 / ST-225 drives are end-of-life.


3270-PC-specific faults:
3270-PC-specific faults:


* '''Keyboard adapter dongle cable''' — wear, missing, or pin damage. Pinout is documented at [http://www.seasip.info/VintagePC/5271.html seasip.info] and reproducible.
* '''Keyboard adapter dongle cable''' — wear, missing, or pin damage. The pinout is documented at seasip.info and is reproducible.<ref name="seasip" />
* '''Custom cards''' — scarce in 2024. The Display Adapter + APA + PSS trio can be transplanted into other XT-class machines provided three adjacent full-length 8-bit ISA slots are available and any onboard video is disabled.
* '''Custom cards''' — scarce in 2024. The Display Adapter + APA + PSS trio can be transplanted into other XT-class machines provided three adjacent full-length 8-bit ISA slots are available and any onboard video is disabled.
* '''IBM 5272 monitor''' — dedicated tube and timings unique to the 3270 PC; failure means substituting a 5151 mono display (losing colour) is the only practical recovery.
* '''IBM 5272 monitor''' — dedicated tube and timings unique to the 3270 PC; failure means substituting a 5151 mono display (losing colour) is the only practical recovery.
* '''Capacitor failure''' — seasip.info documents a real-world case of a blown capacitor taking out a 5271 planar.
* '''Capacitor failure''' — seasip.info documents a 5271 planar that "failed with a blown capacitor".<ref name="seasip" />


== Gallery ==
== Gallery ==
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== References ==
== References ==


* [https://en.wikipedia.org/wiki/IBM_3270_PC IBM 3270 PC — Wikipedia]. Authoritative model reference, pricing, announcement letters.
<references />
* [http://www.seasip.info/VintagePC/5271.html John Elliott, seasip.info — IBM 5271 (3270 PC)]. The most thorough community technical reference.
 
* [https://sharktastica.co.uk/resources/docs/IBM_183-129_3270PC_83.pdf IBM Announcement Letter 183-129 (3270 PC, 18 October 1983)].
=== Further reading ===
* [http://www-01.ibm.com/common/ssi/rep_ca/6/897/ENUS184-136/index.html IBM Announcement Letter 184-136 (1984 IBM 3295 Plasma extension)].
 
* [http://www-01.ibm.com/common/ssi/printableversion.wss?docURL=/common/ssi/rep_ca/3/897/ENUS186-053/index.html IBM Announcement Letter 186-053 (1986 XMA / 30 / 50 / 70 series)].
* [[IBM 3270 PC Maintenance Information]] and [[IBM Personal Computer Family Service Information Manual]] — both hosted here, and the two documents this page is built on.
* [http://bitsavers.org/pdf/ibm/pc/SA38-0037-00_Personal_Computer_Family_Service_Information_Manual_Jul89.pdf IBM SA38-0037-00 Personal Computer Family Service Information Manual (July 1989)], Chapter 10 — 3270 PC service procedures.
* [http://bitsavers.org/pdf/ibm/pc/3270/G320-9539-0_IBM_3270_Personal_Computer_Hints_and_Tips_198605.pdf IBM G320-9539-0 — 3270 Personal Computer Hints and Tips (June 1986)].
* [http://bitsavers.org/pdf/ibm/pc/3270/G320-9539-0_IBM_3270_Personal_Computer_Hints_and_Tips_198605.pdf IBM G320-9539-0 — 3270 Personal Computer Hints and Tips (June 1986)].
* [http://bitsavers.trailing-edge.com/pdf/ibm/pc/cards/1502336_PC_3278_79_Emulation_Adapter_Technical_Adapter_Oct83.pdf IBM 1502336 — PC 3278/79 Emulation Adapter Technical Reference (October 1983)].
* [https://www.bitsavers.org/pdf/ibm/pc/3270/84X0982_3270_Workstation_Program_V1.0_Users_Guide_and_Reference_Apr87.pdf IBM 84X0982 — 3270 Workstation Program v1.0 User's Guide (April 1987)]. The Control Program's software-only successor.
* [https://www.stanislavs.org/helppc/diagnostic_codes.html HelpPC — IBM PC diagnostic codes]. 28xx / 32xx code ranges.


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Latest revision as of 22:03, 24 September 2026

IBM 3270 PC
IBM 3270 PC (machine type 5271) — XT-based mainframe-terminal-emulation workstation, announced 18 October 1983
Specifications
DeveloperIBM Entry Systems Division, Boca Raton, in cooperation with IBM 3270 terminal groups
ManufacturerIBM
TypeMainframe-terminal-emulation workstation (PC XT chassis + 3270 hardware)
Released18 October 1983 (announcement letter 183-129)
Discontinued1987 (superseded by IBM 3270 Workstation Program software running on standard PCs and PS/2s)
CPUIntel 8088 @ 4.77 MHz — identical to the IBM PC XT planar
Memory256 KB on the system board on Models 002, 004, 006, 024, 026, 031, 051 and 071; 640 KB on the system board on Models 030, 050 and 070. Models 004, 006, 024, 026 and 051 add a Printer/Memory Adapter carrying a further 128 KB; Models 031, 051 and 071 carry an Expanded Memory Adapter (XMA) with 1 MB
Storage5.25-inch 360 KB diskette drive (full-height on Models 002–026, half-high on Models 030 onwards), one or two. 10 MB fixed disk on Models 006 and 026; 20 MB on Models 070 and 071 only — Models 030 and 050 are diskette-only
DisplayIBM 5272 Color Display (14" tilt/swivel, 720×350, 7 colours, 24 kHz hsync), or IBM 5151 monochrome, or IBM 3295 Plasma Monitor (Models 24/26)
SoundPC speaker
OS / Firmware3270 PC Control Program + PC DOS 2.0 / 2.1. Control Program v3.0 required for Models 31/51/71 and all P-models. Up to 4 mainframe sessions + 1 DOS task + 2 notepads simultaneously in a windowed display. Single DOS task only. Superseded in 1987 by the 3270 Workstation Program
PredecessorIBM PC XT (5160) (chassis) and IBM 3278 / 3279 terminals (function)
SuccessorIBM 3270 Workstation Program (1987) — same multi-session experience on a standard XT/AT with only a 3278/79 emulation card
Model no.5271 (system unit machine type). Submodels 002, 004, 006, 024, 026, 030, 031, 050, 051, 070, 071, and the P variants P30, P31, P50, P51, P70 and P71, which swap the 5271 keyboard for the 101-key Enhanced Keyboard and a Cable Adapter and require Control Program 3.0

The IBM 3270 PC (machine type 5271) is a mainframe-terminal-emulation workstation announced by IBM on 18 October 1983 (announcement letter 183-129).[1] The system unit is an IBM PC XT (5160) with the expansion slots almost entirely occupied by specialist 3270 cards. IBM says so itself, in the parts catalogue: "all base system parts for the 3270 XT products are the same as 5160 XT base system parts".[2] That is the single most useful fact about servicing one — planar, power supply, drives, covers and keyboard cable are all XT parts, and only the 3270 cards and the displays are unique. The combination of these cards plus the 3270 PC Control Program allows the workstation to host up to four mainframe terminal sessions, one DOS task, and two notepads simultaneously in a windowed display — a unique capability in 1983.[3]

The 3270 PC was discontinued in 1987 when IBM released the 3270 Workstation Program (a software-only product that ran on standard PCs/PS/2s with only a 3278/79 Emulation Adapter), removing the need for the 3270 PC's specialised cards.

Note on Machine-Type Confusion

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The "3270 PC" family includes:

  • IBM 3270 PC (this page) — system unit 5271, the XT-based original.
  • IBM 3270 PC/G — system unit 5371, graphics version with IBM 5278 Display Attachment Unit and IBM 5279 14" display.
  • IBM 3270 PC/GX — also system unit 5371 (not 5372 — both /G and /GX share the same system unit type; the /GX is differentiated by the IBM 5378 Display Attachment Unit and IBM 5379 19" display).
  • IBM PC AT/G and AT/GX — system unit 5373, AT-based equivalents.

Models

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IBM's own model list, from chapter 10 of the Service Information Manual. Read it as a list of what is fitted rather than as a spec ladder — the memory is split between the system board and adapter cards in a way that catches people out.[2]

IBM 3270 PC (5271) models
Model System board RAM Display adapter Diskette Fixed disk Other
002 256 KB 5151/5272 1 × 360 KB — 5271 Keyboard and Keyboard Adapter; 3270 Systems Adapter (DFCA)
004 256 KB 5151/5272 2 × 360 KB — Printer/Memory Adapter with 128 KB
006 256 KB 5151/5272 1 × 360 KB 10 MB Printer/Memory Adapter with 128 KB
024 256 KB 3295 Plasma 2 × 360 KB — Plasma Keyboard Adapter; Printer/Memory Adapter with 128 KB
026 256 KB 3295 Plasma 1 × 360 KB 10 MB Plasma Keyboard Adapter; Printer/Memory Adapter with 128 KB
030 640 KB 5151/5272 1 × 360 KB half-high — Printer Adapter
050 640 KB 5151/5272 2 × 360 KB half-high —
070 640 KB 5151/5272 1 × 360 KB half-high 20 MB
031 256 KB 5151/5272 1 × 360 KB half-high — XMA with 1 MB (includes Printer Adapter); needs Control Program 3.0
051 256 KB 5151/5272 2 × 360 KB half-high — XMA with 1 MB; Printer/Memory Adapter with 128 KB; Control Program 3.0
071 256 KB 5151/5272 1 × 360 KB half-high 20 MB XMA with 1 MB; Control Program 3.0
P30, P31, P50, P51, P70, P71 As the corresponding numeric model, except that an Enhanced (101-key) Keyboard and a Cable Adapter replace the 5271 Keyboard. All P models require Control Program 3.0.

Three things in that table are commonly got wrong:

  • Only Models 070 and 071 have the 20 MB fixed disk. Models 030 and 050 are diskette-only despite being in the same 1986 group.
  • The XMA carries 1 MB, not 2 MB.
  • Models 024 and 026 use a different keyboard adapter — IBM calls it the Plasma Keyboard Adapter — alongside the 3295 Plasma Display Adapter. A standard Keyboard Adapter is not a substitute.

IBM also records a documented trap for the XMA: jumpered as LPT2 on a 5271 with a fixed disk, the XMA is not supported — there is an interrupt-level conflict.[2]

Launch Pricing

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  • Model 006 (256 KB system board plus a 128 KB Printer/Memory Adapter, with the 10 MB fixed disk): $6,210 for the system unit alone.[3]
  • Typical working colour-monitor configuration: about $8,465 including software and cabling.[4]

Specialist Cards

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The 3270 PC system unit is fundamentally an XT 5160 motherboard / chassis / PSU; the difference from a stock XT is in the cards that occupy nearly all eight ISA slots:

Keyboard Adapter Card

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  • Intercepts the 122-key IBM 5271 Keyboard Element scancodes and translates them to XT scancodes.
  • Two variants:
Simple (ROM 6323581)
Complicated (ROM 6323582) — adds NMI button and serial port.
  • Critical: this card holds the video BIOS for the 3270 PC Display Adapter — the video cards do not work without the keyboard adapter card installed.[5]
  • On Models 024 and 026, which drive the 3295 Plasma Monitor, IBM fits a Plasma Keyboard Adapter in place of the standard one.[2]

3270 PC Display Adapter

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  • Main video card, full-length 8-bit ISA.
  • SCN2672 Programmable Video Timing Controller (PVTC) at I/O ports 0180h–019Bh.
  • 8 KB framebuffer split: 4 KB for the 3270-emulation layer / 4 KB for an emulated CGA-or-MDA layer.
  • Drives a unique 720 × 350 mode on the IBM 5272 colour monitor.

All Points Addressable (APA) Card

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  • Optional add-on.
  • Adds CGA-compatible 320 × 200 / 640 × 200 modes plus two 3270-PC-unique graphics modes.
  • Required for graphics-capable mainframe applications.

Programmed Symbols (PSS) Card

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  • Optional add-on.
  • RAM-loaded character sets (up to seven fonts) for 3270 graphics applications.
  • Three of the fonts (4, 5, 7) are tri-plane allowing 8-colour characters.

3278/79 Host Connect / Emulation Adapter

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  • IBM calls this card the DFCA — Distributed Function Communications Adapter — and that is the name the diagnostics and the FRU tables use.[2][6]
  • Coaxial connection to an IBM 3274 (later 3174) control unit. It is coax, not twinax — twinax is the midrange 5250 attachment and will not work here — and the link is point to point, one control-unit port per workstation, with no terminator.[6][2]
  • Two variants exist:
Older — 4 KB buffer, I/O at 2D0h–2D6h.
Newer — adds register at 2D7h; reconfigurable buffer size.
  • Technical reference: IBM 1502336 — PC 3278/79 Emulation Adapter Technical Reference (October 1983), at bitsavers.org/pdf/ibm/pc/cards/.
IBM 5271 (3270 PC) physical layout diagram showing slot placement for the keyboard adapter, display adapter, host-connect card, and the optional APA / PSS expansion cards. (Image: Wikimedia Commons, public domain)

Operating Environment

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The 3270 PC runs PC DOS 2.0 or 2.1 overlaid with the 3270 PC Control Program:

  • Up to 4 mainframe sessions running concurrently.
  • 1 DOS task running concurrently with the mainframe sessions (only one DOS task can be active at a time).
  • 2 notepads for cross-session text manipulation.
  • All seven of these contexts visible in a windowed display on the 5272 monitor.

PC Magazine (January 1985) called the Control Program "a memory hog" — it consumes approximately 200 KB resident, leaving limited free RAM for DOS applications.

Control Program v3.0 is required for the 1986 Models 31/51/71 and all P-models.

In 1987 the 3270 Workstation Program (IBM 84X0982) replaced the Control Program, providing the same multi-session experience on a standard XT or AT with only a 3278/79 Emulation Adapter — and adding DOS 3.3 support plus up to six DOS sessions.[7]

File Transfer

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The 3270 PC's stand-out practical capability is its SEND / RECEIVE file transfer between CMS (or TSO) on the mainframe and PC DOS on the workstation, with automatic EBCDIC↔ASCII conversion.

Display

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  • IBM 5272 Color Display — 14" tilt/swivel, 720 × 350 in 7 colours (no high-intensity; bright and standard CGA colours render identically). Pin 4 of the DE-9 selects mono vs colour. Color timings: hsync 24 kHz negative, vsync 63 Hz negative. Mono timings: 18.6 kHz / 50 Hz.[5]
  • IBM 5151 monochrome — also supported (the graphics card auto-detects monitor type via pin 4).
  • IBM 3295 Plasma Monitor — orange plasma, 62 × 160 or 46 × 106 text grids, supported on Models 24/26.

Keyboard

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The defining accessory of the 3270 PC family is the IBM 5271 Keyboard Element — IBM part 6110344. It is the 122-key Model F terminal keyboard:

  • 24 PF (Program Function) keys.
  • Weight: 9.3 lb (much heavier than a standard PC keyboard).
  • AT protocol, scan code set 3.
  • First announced October 1983; shipped Q1 1984.[8] IBM's own parts catalogue lists keyboard part 6110344 for the 5271 in Figure 7 of the maintenance manual.[6]

The keyboard connects to the keyboard adapter dongle — a small cable that splits a DE-9 on the keyboard controller card into two 5-pin DIN connectors (one for the 3270 keyboard, one passing through to the planar XT keyboard socket).

A plain XT 83-key keyboard works but produces POST error 302 (press F1 to continue). P-model variants use the 101-key Enhanced AT-style keyboard instead.

The IBM 122-key Model F keyboard (IBM part 6110344) — the 5271 Keyboard Element used on all 3270 PC family machines. (Image: Wikimedia Commons, CC BY-SA 4.0)

What IBM's Error Codes Point At

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The 3270 PC posts error codes in ranges that a plain XT does not use, and IBM publishes the mapping from code range to field-replaceable unit:[2]

3270 unique error codes and the FRU each range indicates
Code range FRU indicated
28XX DFCA card (the 3278/79 Emulation Adapter)
32XX Display Adapter card, Programmed Symbols Adapter card, All-Points-Addressable Adapter card, Extended Graphics Adapter card (3270 PC AT only), or the Top Card Connector
44XX Display Attachment Unit — the 5278 with its 5279, or the 5378 with its 5379 (3270 PC/G and /GX)
45XX IEEE Interface Adapter card (IEEE-488)

Two documented traps in that table:

  • A 2801 can be false. If a long DFCA has been replaced with the newer short adapter card, the Keyboard Timer Adapter may also need changing. If you get a 2801, press F1 to continue after POST, and the host session then establishes normally, the 2801 is false. IBM's ECA001 directs the engineer to order P/N 1497249 (one EPROM) and replace the pluggable EPROM on the Keyboard Timer Adapter.[2]
  • The XMA can post a false 8505. The diagnostic for the XMA (P/N 4466857 with piggy-back memory P/N 4466858) tests the D000–DFFF address range; any other adapter with RAM or ROS in that range produces a false 8505.[2]

The coaxial link has its own isolation chart in the maintenance manual, and it ends in a measurement worth knowing: with the machine powered off and the cable disconnected, the resistance at the system unit's coax connector should be less than 1 ohm. If it is not, IBM's instruction is to replace the DFCA.[6] IBM also warns, twice, not to connect or disconnect the coaxial cable during an electrical storm — the cable run to the control unit can be long and is often between buildings.[6]

Common Faults

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The chassis is a stock IBM PC XT — IBM says so in its own parts catalogue[2] — so chassis faults are XT faults:

  • RIFA-branded X / Y mains-suppression caps in the PSU — vent and produce smoke / fish odour. Replace immediately.
  • Tantalum bypass capacitor shorts on the planar — these pull the +5 V rail down. The 5160 board carries sixteen tantalums, thirteen of them on +5 V, and they fail at or shortly after power-on.[9]
  • Hard disk failure on Model 6 / 30 / 50 / 70 — original ST-412 / ST-225 drives are end-of-life.

3270-PC-specific faults:

  • Keyboard adapter dongle cable — wear, missing, or pin damage. The pinout is documented at seasip.info and is reproducible.[5]
  • Custom cards — scarce in 2024. The Display Adapter + APA + PSS trio can be transplanted into other XT-class machines provided three adjacent full-length 8-bit ISA slots are available and any onboard video is disabled.
  • IBM 5272 monitor — dedicated tube and timings unique to the 3270 PC; failure means substituting a 5151 mono display (losing colour) is the only practical recovery.
  • Capacitor failure — seasip.info documents a 5271 planar that "failed with a blown capacitor".[5]
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  • IBM 3270 PC (5271)
    IBM 3270 PC (5271)
  • 3270 PC with display
    3270 PC with display
  • 3270 PC XT colour configuration
    3270 PC XT colour configuration
  • 5271 physical layout diagram
    5271 physical layout diagram
  • 5271 Keyboard Element (122-key Model F)
    5271 Keyboard Element (122-key Model F)
  • 122-key keyboard alternate angle
    122-key keyboard alternate angle
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References

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  1. ↑ IBM Announcement Letter 183-129, 18 October 1983, mirrored at sharktastica.co.uk/resources/docs/IBM_183-129_3270PC_83.pdf.
  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. ↑ 3.0 3.1 Wikipedia, "IBM 3270 PC". Tertiary; used for the launch and withdrawal chronology and the retail prices.
  4. ↑ PC Magazine, 22 January 1985, Valenzuela review of the 3270 PC. Also the source of the "memory hog" characterisation of the Control Program.
  5. ↑ 5.0 5.1 5.2 5.3 John Elliott, The IBM 5271 (aka 3270 PC), seasip.info. A community technical reference built from a working machine: the card complement and what each card does, the video BIOS living in the keyboard controller ROM (part 6323581 for the "simple" controller and 6323582 for the "complicated" one), the error codes 3201, 3202, 3203 and 2801, the 5272 display timings, and the statement that the case, motherboard, drives and power supply are all identical or very similar to the XT.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 IBM, IBM 3270 Personal Computer Maintenance Information, SY27-2567-2, third edition, October 1984 — hosted on this wiki as IBM 3270 PC Maintenance Information. The safety inspection checklist; the problem isolation charts, including the coaxial cable connection test and the coaxial cable resistance check; section 4, locations, including the system board diagram; section 5, removal, replacement and adjustments; and section 7, the illustrated parts catalogue for the 5271 system unit, the 5161 Expansion Unit, the 5151 Monochrome Display, the 5272 Color Display and the keyboard.
  7. ↑ IBM, 3270 Workstation Program Version 1.0 User's Guide and Reference, 84X0982, April 1987, at bitsavers.org/pdf/ibm/pc/3270/.
  8. ↑ sharktastica.co.uk — IBM Model F and deskthority — IBM Model F 122-key. Community keyboard references; the source for the 9.3 lb weight and the scan-code-set-3 behaviour.
  9. ↑ Commonly Failing Electronic Components (in vintage computers) and Short-circuit on the +5 volt line of an IBM 5150/5155/5160 motherboard, minuszerodegrees.net. Sources for the tantalum failure modes on 51xx boards and for the count of sixteen tantalums on the 5160 motherboard, thirteen of them on the +5 V line. Community sources that mirror IBM data; they apply to the 3270 PC because IBM states the base system parts are the same as the 5160 XT's.

Further reading

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