Editing IBM PC (5150)

{{Infobox computer
| name          = IBM Personal Computer
| logo          = [[File:IBM PC 5150 badge.svg|150px]]
| image         = [[File:IBM 5150 PC.jpg|260px]]
| caption       = IBM 5150 Personal Computer with 5151 monochrome display and Model F keyboard
| developer     = IBM Entry Systems Division, Boca Raton
| manufacturer  = IBM
| type          = Desktop personal computer
| release date  = August 12, 1981
| discontinued  = April 2, 1987
| price         = US$1,565 (base, 16 KB, no FDD); typical home/school system around US$3,000
| cpu           = Intel 8088 @ 4.77 MHz<br/>Optional Intel 8087 FPU
| memory        = Early board: 16-64 KB on-board<br/>Later board: 64-256 KB on-board<br/>Expandable to 640 KB via ISA RAM cards
| storage       = Cassette port; one or two 5.25" floppy drives ([[Tandon TM100-1|TM100-1]] single-sided 160 KB; [[Tandon TM100-2|TM100-2]] double-sided 320/360 KB)
| display       = [[IBM Monochrome Display Adapter|MDA]] + [[IBM 5151]] monochrome display, or [[IBM Color Graphics Adapter|CGA]] + [[IBM 5153]] colour display (separate adapter card)
| sound         = Internal PC speaker, driven by Intel 8253-5 timer channel 2
| dimensions    = 20" W × 16" D × 5.5" H
| weight        = 21 lb (no FDD); 25 lb (one FDD); 28 lb (two FDDs)
| os            = IBM PC DOS 1.0 through PC DOS 3.3; CP/M-86; UCSD p-System; [[IBM Cassette BASIC]] in ROM
| successor     = [[IBM PC XT (5160)]]
| codename      = Acorn (development project name)
| model         = 5150
}}

The '''IBM Personal Computer''' (model '''5150''') is the original IBM PC, announced on August 12, 1981 and shipped from September 1981 through April 2, 1987. It was developed in roughly one year by a team in Boca Raton, Florida under Don Estridge and William C. Lowe, using off-the-shelf parts to bring an IBM-branded microcomputer to market quickly. The architecture it established — Intel 8088 CPU, 8-bit ISA expansion bus, MS-DOS, an open BIOS interface, and Microsoft Disk BASIC in ROM — became the standard for personal computers for the following two decades.

== Architecture and Processor ==
The 5150 uses an '''Intel 8088''' running at '''4.77 MHz''', a 16-bit CPU with an 8-bit external data bus. A second socket on the motherboard accepts an '''Intel 8087''' floating-point coprocessor, sold separately.

The CPU is supported by the IBM 8088-family chipset:
* '''Intel 8259A''' — programmable interrupt controller.
* '''Intel 8237A-5''' — DMA controller, also responsible for DRAM refresh.
* '''Intel 8253-5''' — programmable interval timer (system tick, refresh trigger, speaker).
* '''Intel 8255A-5''' — programmable peripheral interface (keyboard input, DIP-switch readback, speaker enable).
* '''Motorola MC6845''' — CRT controller, on the [[IBM Monochrome Display Adapter|MDA]] and [[IBM Color Graphics Adapter|CGA]] display adapters, not on the motherboard.

== Memory and ROM ==
Two motherboard revisions exist, distinguished by the amount of on-board RAM they accept and clearly marked in the silkscreen near the keyboard port.

<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:70%; text-align:center;"
|+'''IBM 5150 motherboard revisions'''
! Silkscreen marking !! On-board RAM !! RAM chip type !! Banks
|-
| 16KB-64KB (early) || 16 KB &ndash; 64 KB || 4116 (16 Kbit, requires &minus;5 V) || 4 × 16 KB
|-
| 64KB-256KB (later) || 64 KB &ndash; 256 KB || 4164 (64 Kbit) || 4 × 64 KB
|}

The motherboard carries ROM in five sockets:
* '''U33''' &mdash; BIOS ROM.
* '''U29, U30, U31, U32''' &mdash; [[IBM Cassette BASIC]] (Microsoft BASIC).

There are four documented BIOS revisions, all dated rather than numbered (date format MM/DD/YY):

{| class="wikitable styled-table" style="width:70%; text-align:center;"
|+'''IBM 5150 BIOS revisions'''
! Date !! IBM part number !! Compatible board !! Notes
|-
| 04/24/81 || 5700051 || 16KB-64KB only || Recognises only 544 KB total RAM; ignores BIOS expansion ROMs (no EGA/VGA, no HDD)
|-
| 10/19/81 || 5700671 || 16KB-64KB only || Same two limitations as 04/24/81
|-
| 08/16/82 || 5000024 || (rare/possibly unreleased) || Has a bug where EGA / 5150-compatible VGA fail if SW1 video bits are set ON-ON
|-
| 10/27/82 || 1501476 || 16KB-64KB or 64KB-256KB || Removes the 1981 BIOS limits; bug: a corrupted HDD expansion ROM at C8000 beeps "1 long + 2 short" instead of displaying "C800 ROM"
|}

System configuration is set by '''two banks of DIP switches''' (SW1 and SW2) on the motherboard. The 5150 has no battery-backed CMOS &mdash; the DIP switches are read at every power-up.

== Storage and Expansion ==
* '''Cassette port''' (5-pin DIN, rear panel) for tape data, paired with the [[IBM Cassette BASIC]] ROM.
* '''Floppy disk drive''' — one or two half-height 5.25" drives: [[Tandon TM100-1]] single-sided (160 KB at PC DOS 1.0; 180 KB at PC DOS 2.0+) on the earliest 5150s, then [[Tandon TM100-2|Tandon TM100-2 / TM100-2A]] or Micropolis 1015-5 double-sided (320 KB at PC DOS 1.1; 360 KB at PC DOS 2.0+). Drives connect to an [[IBM FDD Adapter|IBM FDD Adapter]] ISA card; the motherboard has no on-board floppy controller.
* '''No internal hard drive support''' from the original 63.5 W Type 1 PSU. The later 130 W Type 2 PSU made it possible to fit an MFM hard drive on an [[IBM Fixed Disk Adapter|IBM Fixed Disk Adapter]].
* '''5 × 8-bit ISA slots.'''

== Display ==
The 5150 has no on-board video. All video is provided by an ISA adapter card driving a separate monitor:
* '''[[IBM Monochrome Display Adapter|IBM Monochrome Display Adapter (MDA)]]''' — 80×25 text only, monochrome; paired with the [[IBM 5151]] green-phosphor monitor.
* '''[[IBM Color Graphics Adapter|IBM Color Graphics Adapter (CGA)]]''' — text and graphics modes; paired with the [[IBM 5153]] colour monitor or any composite TV.

== Keyboard ==
The 5150 ships with the '''[[IBM Model F (83-key)]]''' XT-layout keyboard — the original capacitive buckling-spring keyboard. It connects to the rear of the case via a 5-pin DIN connector. Unlike later AT-class machines, the '''5150 has no keyboard controller IC on the motherboard''' — the keyboard interface is read by the 8255 PPI.

== Power Supply ==
Two PSU revisions exist:
* '''Type 1''' — 63.5 W, sufficient for the base configuration of motherboard + floppy drive(s).
* '''Type 2''' — 130 W, introduced to support an internal hard drive.

Both produce '''+5 V, +12 V, &minus;5 V, &minus;12 V''' on the motherboard's P8/P9 connectors. The &minus;5 V rail is required by the 4116 DRAM on the early 16KB-64KB board, and by the cassette circuitry on the later 64KB-256KB board.

== General Maintenance ==
Cleaning procedures, PSU voltage checks, and preventive care are documented in [[IBM PC (5150) Maintenance Guide]].

== Capacitor Replacement Guide ==
The 5150 uses tantalum capacitors on the motherboard and ISA cards. Short-circuit tantalum failure is one of the most common faults on this machine. Procedures and the verified motherboard capacitor information are at [[IBM PC (5150) Capacitor Replacement Guide]].

== Troubleshooting ==
POST beep codes, parity errors, RAM bank 0 failure, keyboard 301 errors, and PSU diagnostics are at [[IBM PC (5150) Troubleshooting Guide]].

== Gallery ==
<gallery mode="packed" heights="200">
File:IBM 5150 PC.jpg|IBM 5150 with 5151 monochrome display and Model F keyboard
File:IBM 5150 Front.jpg|IBM 5150 front view, 5.25" twin-floppy configuration
</gallery>

== Related Pages ==
* [[IBM PC (5150) Maintenance Guide]]
* [[IBM PC (5150) Troubleshooting Guide]]
* [[IBM PC (5150) Capacitor Replacement Guide]]
* [[IBM PC XT (5160)]] — immediate successor
* [[IBM Monochrome Display Adapter]] / [[IBM Color Graphics Adapter]]
* [[IBM Model F (83-key)]]

== References ==

* IBM, ''IBM 5150 Technical Reference'' (part 6025005, August 1981) [https://www.minuszerodegrees.net/manuals/IBM_5150_Technical_Reference_6025005_AUG81.pdf — bitsavers/minuszerodegrees mirror].
* "IBM Personal Computer" — Wikipedia.
* [https://minuszerodegrees.net/5150/bios/5150_bios_revisions.htm 5150 BIOS Revisions], minuszerodegrees.net.
* [https://www.minuszerodegrees.net/5150/motherboard/5150_motherboard_revisions.htm 5150 Motherboard Revisions], minuszerodegrees.net.
* [https://oldcomputers.net/ibm5150.html IBM 5150 Personal Computer], OldComputers.net (dimensions and weight).

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[[Category:IBM]]