IBM PC (5150): Difference between revisions
Rebuilt against IBM's 5150 Technical Reference (hosted here) and minuszerodegrees. The big correction: there was never a 130 W 'Type 2' power supply for the 5150 - the supply is ~63 W throughout, IBM put the 130 W unit in the XT for exactly this reason, and IBM's own hard-disk answer for the 5150 was the 5161 Expansion Unit. Also: three released BIOS revisions plus an 08/16/82 that may never have shipped (not 'four documented'); the 10/27/82 BIOS requires all four RAM banks populated; five RO... |
P4 verification: link the IBM manuals hosted on this wiki that document this machine (they were unlinked from every article) |
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* [[IBM Model F (83-key)]] · [[IBM Cassette BASIC]] · [[IBM 5151]] · [[IBM 5153]] | * [[IBM Model F (83-key)]] · [[IBM Cassette BASIC]] · [[IBM 5151]] · [[IBM 5153]] | ||
* [[IBM PC 5150 Technical Reference]] — IBM's own reference, hosted here | * [[IBM PC 5150 Technical Reference]] — IBM's own reference, hosted here | ||
* '''IBM documentation hosted here:''' [[IBM PC 5150 Technical Reference]] · [[IBM PC BASIC Reference (May 1984)]] · [[IBM PC BASIC Quick Reference (May 1984)]] · [[IBM PS2 and PC BIOS Interface Technical Reference]] · [[IBM Technical Directory PC and PS2 (June 1988)]] | |||
{{Navbox-IBMComputers|state=collapsed}} | {{Navbox-IBMComputers|state=collapsed}} | ||
[[Category:IBM]] | [[Category:IBM]] | ||
Revision as of 00:19, 25 September 2026
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| IBM 5150 Personal Computer with 5151 monochrome display and 83-key keyboard | |
| Specifications | |
|---|---|
| Developer | IBM Entry Systems Division, Boca Raton |
| Manufacturer | IBM |
| Type | Desktop personal computer |
| Released | August 1981 |
| Discontinued | 1987 |
| CPU | Intel 8088 @ 4.77 MHz; optional Intel 8087 coprocessor |
| Memory | 16–64 KB on the early system board; 64–256 KB on the later one; expandable on the I/O channel |
| Storage | Cassette port; one or two 5.25" diskette drives on an adapter card |
| Display | MDA with an IBM 5151, or CGA with an IBM 5153 — on an adapter card, not on the board |
| Sound | Speaker driven by channel 2 of the 8253-5 timer |
| OS / Firmware | IBM PC DOS; CP/M-86; UCSD p-System; IBM Cassette BASIC in ROM |
| Successor | IBM PC XT (5160) |
| Model no. | 5150 |
The IBM Personal Computer, model 5150, is the machine that set the shape of the PC industry: an Intel 8088, an open 8-bit I/O channel, a documented BIOS, and Microsoft BASIC in ROM. This page covers what a restorer needs — the two board revisions, the BIOS revisions and their bugs, the power supply's real ratings, and the traps that make a healthy 5150 look dead.
System Board
The 8088 runs at 4.77 MHz, with a socket for an Intel 8087 coprocessor. Support devices on the board are the 8259A interrupt controller, the 8237A-5 DMA controller (which also does DRAM refresh), the 8253-5 timer and the 8255A-5 peripheral interface.
Five 62-pin card-edge sockets carry the I/O channel: five expansion slots. DC power arrives on two six-pin connectors, and the board also carries the keyboard, cassette and speaker connections.[1]
There is no keyboard controller chip. The keyboard interface is handled by the 8255 peripheral interface and a latch; there is no 8042 on this machine.[1] There is also no real-time clock and no battery-backed CMOS: two eight-switch DIP packs, SW1 and SW2, tell the BIOS how much memory is fitted, what display adapter is installed, how many diskette drives are attached and what mode to start in.[1]
Of the eight prioritised interrupt levels, six are bussed to the expansion slots. Level 0 is the timer tick and level 1 is the keyboard; the 8088's non-maskable interrupt reports memory parity errors.[1]
Board revisions
Two revisions exist, distinguished by the silkscreen next to the keyboard connector and by nothing else that matters:[2]
| Silkscreen | On-board RAM | Banks | BIOS as supplied |
|---|---|---|---|
| "16KB-64KB CPU" | 16–64 KB | 4 banks of 16 KB (4116-class, needs −5 V) | 04/24/81 or 10/19/81 |
| "64KB-256KB CPU" | 64–256 KB | 4 banks of 64 KB (64K×1) | 10/27/82 |
On the later board, bank 0 is soldered and banks 1 to 3 are socketed. All memory is parity-checked; the chips are 250 ns access, 410 ns cycle.[1]
ROM
Six module sockets are provided, each taking an 8 KB device; five are populated, giving 40 KB.[1] U33 holds the BIOS; U29, U30, U31 and U32 hold IBM Cassette BASIC and nothing else. The ROM is 250 ns access, 375 ns cycle.[1]
BIOS revisions
Three revisions were released, plus one that may never have reached the public. There are no version numbers — only dates, in MM/DD/YY form.[3]
| Date | IBM part number | Boards | Notes |
|---|---|---|---|
| 04/24/81 | 5700051 | 16KB-64KB only | Recognises at most 544 KB of RAM, and does not recognise BIOS expansion ROMs on cards — so no EGA, no VGA and no hard disk controller |
| 10/19/81 | 5700671 | 16KB-64KB only | The same two limitations |
| 08/16/82 | 5000024 | — | May not have been publicly released. EGA and 5150-compatible VGA cards fail if the SW1 video switches are set ON-ON, but work at OFF-OFF |
| 10/27/82 | 1501476 | both | Removes the 1981 limitations. Requires all four banks of system-board RAM to be populated, with SW1 and SW2 set accordingly, because of bugs in its memory sizing |
That last requirement catches people upgrading a 16KB-64KB board to the 10/27/82 BIOS.[3]
The 10/27/82 BIOS also carries a bug worth knowing before you diagnose a video fault: if a hard disk controller's expansion ROM at C8000 is corrupted anywhere except its first two bytes, the POST is supposed to display "C800 ROM", but instead beeps one long and two short — the pattern that normally means a video problem.[4]
Storage and Expansion
- Cassette port — a 5-pin DIN on the rear panel, paired with IBM Cassette BASIC. The cable is the same one the Radio Shack TRS-80 used.
- Diskette — one or two 5.25-inch drives on an IBM 5-1/4" Diskette Drive Adapter card; there is no diskette controller on the system board. Early machines got the single-sided Tandon TM100-1; later ones the double-sided Tandon TM100-2 / TM100-2A or the Micropolis equivalent.[4] The IBM controller and all three BIOS revisions support 160/180 KB and 320/360 KB drives fully, support 720 KB drives for reading and writing but not formatting, and do not support 1.2 MB or 1.44 MB at all.[5]
- Hard disk — see below.
- Expansion — five 8-bit slots. Some 16-bit cards sold as "8-bit slot compatible" mean an 8-bit slot in an AT-class machine and will not work here; others need reconfiguring for 8-bit operation by switch, jumper or software.[4]
Hard disks, and the 130 W supply that never existed
IBM never offered a 130 W power supply for the 5150. The machine's supply is rated at about 63 W throughout its life, and that is the reason IBM fitted a 130 W supply to the IBM PC XT (5160) instead: the +12 V start-up demand of a Seagate ST-412 comfortably exceeds the 24 W the 5150's +12 V rail can provide.[6]
IBM's own hard-disk answer for the 5150 was the 5161 Expansion Unit — a separate box with its own supply, containing the drive and controller.[6]
From 1983, a 5150 with the 10/27/82 BIOS could take an XT-class controller such as the IBM Fixed Disk Adapter and run DOS 2, and the only question was whether the supply would cope. Later, smaller drives such as the Seagate ST-225 are reported to work on the 63 W supply.[6] That is an owner's judgement about a specific drive, not an IBM configuration.
Display
The 5150 has no video on the system board. All video is on a card:
- MDA — 80 × 25 text only, with the parallel printer port on the same card, driving an IBM 5151.
- CGA — text and graphics, driving an IBM 5153, a composite monitor or a television through an RF modulator.
The SW1 video switches must match the card fitted. Getting them wrong leaves the adapter uninitialised, which on a 5151 produces no raster at all and looks exactly like a dead monitor.[7]
Keyboard
The 5150 ships with the 83-key keyboard, a capacitive buckling-spring design with an Intel 8048 inside and a permanently attached coiled cable to a 5-pin DIN.[1] An AT-protocol keyboard will not work on a 5150 without a converter.[8]
Power Supply
One supply, not two. IBM's Technical Reference rates it for continuous operation at 63.5 W, with a fused 120 Vac or 220/240 Vac input and four regulated dc outputs.[1] In practice 110 V units are usually labelled 63.5 W and 220 V units 63 W.[9]
| Rail | Min load | Max load | Regulation | Under-voltage sense | Over-voltage sense |
|---|---|---|---|---|---|
| +5 Vdc | 2.3 A | 7.0 A | +5% / −4% | +4.0 V | +5.9 V |
| −5 Vdc | 0.0 A | 0.3 A | +10% / −8% | −4.0 V | −5.9 V |
| +12 Vdc | 0.4 A | 2.0 A | +5% / −4% | +9.6 V | +14.2 V |
| −12 Vdc | 0.0 A | 0.25 A | +10% / −9% | −9.6 V | −14.2 V |
The +5 V rail powers the board and drives and leaves about 4 A for adapter cards. +12 V runs the dynamic memory and both diskette drive motors, on the assumption that only one is active at a time. All four rails are bussed across all five slots.[1]
The supply also provides a filtered, fused, switched ac outlet at the rear, limited to 0.75 A, on a non-standard connector intended only for the IBM 5151.[1]
Protection: on over-voltage the supply shuts every output down when +5 V or +12 V exceeds 200 % of its maximum rated voltage; on over-current it turns off if any output exceeds 130 % of nominal. The primary is fused at 2 A (120 V) or 1 A (220/240 V).[1]
Switch the machine off for at least five seconds before switching it on again. IBM's 'power good' signal is only generated after a five-second off period, and it has a 100 ms turn-on delay after the rails reach their sense levels. A faster cycle can leave the board without 'power good' and looking dead.[1][9]
The supply also needs a minimum load to start. A working system board alone is normally enough; so is a working full-height Tandon drive. "Normally" is not "always", and an overloaded supply produces the same symptoms — fan turning for a second and stopping, or not turning at all.[9]
What −5 V is actually for
IBM calls it the "dynamic memory bias voltage": it tracks +5 V and +12 V quickly at power-on and decays more slowly at power-off.[1] Known IBM uses:[9]
- The 4116-class RAM on the 16KB-64KB board.
- Chip U1 on both board revisions.
- The IBM 32 KB and 64 KB Memory Expansion Options.
- Early versions of the IBM 5.25" Diskette Drive Adapter.
This matters if you power a bare board from a modern ATX supply with no −5 V: a 16KB-64KB board simply appears dead, because the POST's first-16 KB RAM test fails and the POST halts with no beep and nothing on screen; a 64KB-256KB board gets as far as a 131 error, because U1 in the cassette circuitry needs −5 V.[4]
Things That Are Not Faults, and Traps
- A POST card shows nothing useful. The 5150's POST does not emit POST codes. Any numbers a POST card displays are something else.[4]
- A "dead" board is usually not dead. A short-circuit tantalum anywhere — system board, card or drive — will stop the supply, though the fan may still turn. A failure of any chip in RAM bank 0 produces the same apparently-dead board. Both are far more common than a genuinely failed board.[4][10]
- One long beep and two short need not mean video. See the C8000 expansion-ROM bug above.[4]
- A card ROM at F0000 to F3FFF will fight the system board. The board decodes that range for reads even though nothing is there, so a card mapped into it causes bus contention — and may appear to work while doing so.[4]
General Maintenance
Cleaning, rail checks and preventive care are in IBM PC (5150) Maintenance Guide.
Capacitor Replacement
The 5150 decouples with tantalum capacitors, on the board and on the cards, and they fail short. The verified information is in IBM PC (5150) Capacitor Replacement Guide.
Troubleshooting
Beep codes, parity errors, bank 0 failures, 301 keyboard errors and supply diagnostics are in IBM PC (5150) Troubleshooting Guide.
Gallery
-
IBM 5150 with a 5151 display and the 83-key keyboard -
Front view, twin diskette drives
References
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 IBM, IBM 5150 Technical Reference — hosted on this wiki as File:IBM PC 5150 Technical Reference.pdf and documented as IBM PC 5150 Technical Reference. Section 1 "System Board" for the ROM and RAM subsystems; Section 3 "Power Supply", pages 3-3 to 3-6, for the 63.5 W continuous rating, the four dc outputs and their load and regulation figures, the −5 V dynamic-memory bias role, the switched 0.75 A ac outlet provided only for the IBM Monochrome Display, the overvoltage and overcurrent behaviour, the five-second minimum off time and the under- and over-voltage sense levels; Section 4 "Keyboard" for the capacitive keyboard, its Intel 8048, the permanently attached coiled five-wire cable, the 83-key layout, the scan-code protocol and the keyboard's own power-on self test.
- ↑ IBM 5170 — Motherboard Versions, minuszerodegrees.net, citing IBM user documentation. Source for the three types, their speeds, form factors, main crystal frequencies, RAM chip types and bank layouts, the BIOS revision supplied with each, the 150 ns RAM access requirement, and the jumper J18 and SETUP follow-up needed when changing the Type 1 board between single-bank and dual-bank operation.
- ↑ 3.0 3.1 IBM 5150 — BIOS Revisions, minuszerodegrees.net. Source for the three released revisions and the 08/16/82 revision that may never have been publicly released, their IBM part numbers, the 544 KB RAM ceiling and lack of BIOS-expansion-ROM support in the 1981 revisions, the EGA/VGA switch-setting bug in the 08/16/82 revision, and the requirement that the 10/27/82 revision have all four RAM banks populated.
- ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 IBM 5150 — Known Problems/Issues, minuszerodegrees.net. Source for the C8000 expansion-ROM bug (a corrupted ROM gives one long and two short beeps instead of the expected "C800 ROM" message), the short-circuit tantalum symptom, the consequences of running the board without −5 V (a dead 16KB-64KB board, a 131 error on a 64KB-256KB board because chip U1 in the cassette circuitry needs it), the bank 0 RAM failure that looks like a dead board, the fact that the 5150's POST emits no POST-card-readable codes, the 16-bit ISA card caveats, and the F0000 to F3FFF decode that causes bus contention with a card ROM mapped there.
- ↑ IBM 5150 — Floppy Drive Support, minuszerodegrees.net. Source for the requirement to use the particular cable that manipulates both the motor-on and drive-select lines, the warning not to substitute the hard-drive type of twisted cable, and the drive and diskette support matrix for the IBM controller and the three 5150 BIOS revisions.
- ↑ 6.0 6.1 6.2 IBM 5150 — Hard Drive Support, minuszerodegrees.net: the 5150's 63 W supply was inadequate for the hard drives of the time, and that "is the reason why IBM put a 130W power supply in the 5160". The page also shows the +12 V start-up demand of the Seagate ST-412 against the 5150's 24 W +12 V rating.
- ↑ IBM 5151 — Known Problems/Issues, minuszerodegrees.net. Source for the stiff brightness and contrast controls being normal, the raster-but-no-video diagnosis, the reported IC201 (SN7406A) failures, the vertical collapse and switch-off bright line notes, the statement that pins 3, 4 and 5 are absent from the connector by design, and the warning that an improper horizontal sync signal can damage the 5151.
- ↑ IBM 5150 — Keyboards, minuszerodegrees.net. Source for IBM's own name for this keyboard ("83-key keyboard"), the type 1 / type 2 distinction in reset behaviour, the point that "Model F" is a family name covering keyboards that will not work with a 5150, the reassembly warning, the cable metering diagram, and the incompatibility of AT-protocol keyboards.
- ↑ 9.0 9.1 9.2 9.3 IBM 5170 — Power Supply Unit, minuszerodegrees.net. Source for the approximate 192 W rating, the per-line rating caveat, the start-up loading behaviour, and the minimum loading figures of 7 A on +5 V and 2.5 A on +12 V taken from the 5170 Technical Reference.
- ↑ Tantalum capacitors on IBM 51xx motherboards/cards, minuszerodegrees.net, together with its 2-legged and 3-legged pages. Source for the 10 µF/16 V value and its "106 16V" markings, the three-hole footprint and its two wiring variants, the negative-positive-negative polarity of the 3-legged variant, and the Kemet/Mouser replacement part numbers. These pages state their scope as the IBM 5150, 5155 and 5160 — not the PCjr.
Related Pages
- IBM PC (5150) Maintenance Guide · IBM PC (5150) Troubleshooting Guide · IBM PC (5150) Capacitor Replacement Guide
- IBM PC XT (5160) — the successor
- IBM Monochrome Display Adapter · IBM Color Graphics Adapter · IBM FDD Adapter · IBM Fixed Disk Adapter
- IBM Model F (83-key) · IBM Cassette BASIC · IBM 5151 · IBM 5153
- IBM PC 5150 Technical Reference — IBM's own reference, hosted here
- IBM documentation hosted here: IBM PC 5150 Technical Reference · IBM PC BASIC Reference (May 1984) · IBM PC BASIC Quick Reference (May 1984) · IBM PS2 and PC BIOS Interface Technical Reference · IBM Technical Directory PC and PS2 (June 1988)