IBM PC AT (5170) - Revision history

Josh: P4 verification: merge the duplicated manual links into one documentation line

2026-09-24T23:20:35Z

P4 verification: merge the duplicated manual links into one documentation line

← Older revision		Revision as of 00:20, 25 September 2026
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	* [[IBM PC (5150)]] · [[IBM PC XT (5160)]]		* [[IBM PC (5150)]] · [[IBM PC XT (5160)]]
	* [[IBM Monochrome Display Adapter]] · [[IBM Color Graphics Adapter]] · [[IBM 5151]] · [[IBM 5153]]		* [[IBM Monochrome Display Adapter]] · [[IBM Color Graphics Adapter]] · [[IBM 5151]] · [[IBM 5153]]
	* [[IBM PC AT 5170 Technical Reference (September 1985)]] · [[IBM Personal Computer Family Service Information Manual]] — IBM's own references, hosted here		* '''IBM documentation hosted here:''' [[IBM PC AT 5170 Technical Reference (March 1984)]] · [[IBM PC AT 5170 Technical Reference (September 1985)]] · [[IBM Personal Computer Family Service Information Manual]] · [[IBM PS2 and PC BIOS Interface Technical Reference]]
	* '''IBM documentation hosted here:''' [[IBM PC AT 5170 Technical Reference (March 1984)]] · [[IBM PC AT 5170 Technical Reference (September 1985)]] · [[IBM PS2 and PC BIOS Interface Technical Reference]]

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	[[Category:IBM]]		[[Category:IBM]]

Josh: P4 verification: link the IBM manuals hosted on this wiki that document this machine (they were unlinked from every article)

2026-09-24T23:19:34Z

P4 verification: link the IBM manuals hosted on this wiki that document this machine (they were unlinked from every article)

← Older revision		Revision as of 00:19, 25 September 2026
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	* [[IBM Monochrome Display Adapter]] · [[IBM Color Graphics Adapter]] · [[IBM 5151]] · [[IBM 5153]]		* [[IBM Monochrome Display Adapter]] · [[IBM Color Graphics Adapter]] · [[IBM 5151]] · [[IBM 5153]]
	* [[IBM PC AT 5170 Technical Reference (September 1985)]] · [[IBM Personal Computer Family Service Information Manual]] — IBM's own references, hosted here		* [[IBM PC AT 5170 Technical Reference (September 1985)]] · [[IBM Personal Computer Family Service Information Manual]] — IBM's own references, hosted here
			* '''IBM documentation hosted here:''' [[IBM PC AT 5170 Technical Reference (March 1984)]] · [[IBM PC AT 5170 Technical Reference (September 1985)]] · [[IBM PS2 and PC BIOS Interface Technical Reference]]

	{{Navbox-IBMComputers\|state=collapsed}}		{{Navbox-IBMComputers\|state=collapsed}}

	[[Category:IBM]]		[[Category:IBM]]

Josh: Rebuilt against IBM's AT Technical Reference and the Personal Computer Family Service Information Manual (both hosted here) plus minuszerodegrees. Corrections: weight is 19.05 kg (42 lb) in IBM's service manual and 20.0 kg (44 lb) in the Technical Reference - both quoted - not '~43 lb (19.5 kg)'; height is 162 mm (IBM prints 6.8 in), not 6.4 in; the eight I/O slots are SIX 16-bit and TWO 8-bit, not eight 16-bit; the 16450 UART belongs to the separate Serial/Parallel Adapter, not the system bo...

2026-09-23T02:39:18Z

Rebuilt against IBM's AT Technical Reference and the Personal Computer Family Service Information Manual (both hosted here) plus minuszerodegrees. Corrections: weight is 19.05 kg (42 lb) in IBM's service manual and 20.0 kg (44 lb) in the Technical Reference - both quoted - not '~43 lb (19.5 kg)'; height is 162 mm (IBM prints 6.8 in), not 6.4 in; the eight I/O slots are SIX 16-bit and TWO 8-bit, not eight 16-bit; the 16450 UART belongs to the separate Serial/Parallel Adapter, not the system bo...

Show changes

Josh: Reduce infobox badge size from 250px to 150px

2026-05-23T16:32:24Z

Reduce infobox badge size from 250px to 150px

← Older revision		Revision as of 17:32, 23 May 2026
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	{{Infobox computer		{{Infobox computer
	\| name = IBM Personal Computer AT		\| name = IBM Personal Computer AT
	\| logo = [[File:IBM PC AT 5170 badge.svg\|~~250px~~]]		\| logo = [[File:IBM PC AT 5170 badge.svg\|150px]]
	\| image = [[File:IBM PC AT 5170.jpg\|260px]]		\| image = [[File:IBM PC AT 5170.jpg\|260px]]
	\| caption = IBM Personal Computer AT (5170)		\| caption = IBM Personal Computer AT (5170)

Josh: Add IBM badge to infobox (logo = File:IBM PC AT 5170 badge.svg)

2026-05-23T16:30:50Z

Add IBM badge to infobox (logo = File:IBM PC AT 5170 badge.svg)

← Older revision		Revision as of 17:30, 23 May 2026
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	{{Infobox computer		{{Infobox computer
	\| name = IBM Personal Computer AT		\| name = IBM Personal Computer AT
			\| logo = [[File:IBM PC AT 5170 badge.svg\|250px]]
	\| image = [[File:IBM PC AT 5170.jpg\|260px]]		\| image = [[File:IBM PC AT 5170.jpg\|260px]]
	\| caption = IBM Personal Computer AT (5170)		\| caption = IBM Personal Computer AT (5170)

Josh: /* Motherboard Revisions */

2026-05-21T10:18:51Z

Motherboard Revisions

← Older revision		Revision as of 11:18, 21 May 2026
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	<templatestyles src="Template:StyledTable/styles.css" />		<templatestyles src="Template:StyledTable/styles.css" />
	{\| class="wikitable styled-table" style="width:~~100~~%; text-align:center;"		{\| class="wikitable styled-table" style="width:70%; text-align:center;"
	\|+'''IBM 5170 motherboard revisions'''		\|+'''IBM 5170 motherboard revisions'''
	! Type !! CPU speed !! Form factor !! On-board RAM !! BIOS shipped !! Main crystal !! Submodels fitted		! Type !! CPU speed !! Form factor !! On-board RAM !! BIOS shipped !! Main crystal !! Submodels fitted
Line 63:		Line 63:
	The 5170 BIOS (including ROM BASIC) is 64 KB. On very early motherboards it shipped as four 16 KB chips (27128) in sockets U17/U27/U37/U47. Later production used two 32 KB chips (27256) in sockets U27 and U47. On Type 1 boards, shunt block U131 selects which ROM type is installed.		The 5170 BIOS (including ROM BASIC) is 64 KB. On very early motherboards it shipped as four 16 KB chips (27128) in sockets U17/U27/U37/U47. Later production used two 32 KB chips (27256) in sockets U27 and U47. On Type 1 boards, shunt block U131 selects which ROM type is installed.

	{\| class="wikitable styled-table" style="width:~~100~~%; text-align:center;"		{\| class="wikitable styled-table" style="width:70%; text-align:center;"
	\|+'''IBM 5170 BIOS revisions'''		\|+'''IBM 5170 BIOS revisions'''
	! Date !! Mask ROM (U27/U47) !! EPROM part numbers !! Motherboard !! Floppy support !! HDD support		! Date !! Mask ROM (U27/U47) !! EPROM part numbers !! Motherboard !! Floppy support !! HDD support

Josh: Create/rewrite IBM PC AT (5170) and IBM PCjr (4860) page set with verified facts, real images, and embedded content per RTC style guide

2026-05-21T10:18:28Z

Create/rewrite IBM PC AT (5170) and IBM PCjr (4860) page set with verified facts, real images, and embedded content per RTC style guide

New page

{{Infobox computer
| name = IBM Personal Computer AT
| image = [[File:IBM PC AT 5170.jpg|260px]]
| caption = IBM Personal Computer AT (5170)
| developer = IBM Entry Systems Division, Boca Raton
| manufacturer = IBM
| type = Desktop personal computer
| release date = August 14, 1984
| discontinued = April 2, 1987 (final units of model 339 left the assembly line in July 1987)
| cpu = Intel 80286 @ 6 MHz (Type 1/2 motherboards) or 8 MHz (Type 3)<br/>Optional Intel 80287 FPU
| memory = 256 KB or 512 KB on-board (depends on motherboard revision); expandable to 16 MB total via 16-bit ISA memory cards
| storage = 1.2 MB 5.25" high-density floppy drive; optional 20 MB or 30 MB MFM hard drive (CMI 5616 or CMI 6426 on early units; later Seagate ST-225/ST-251)
| display = [[IBM Monochrome Display Adapter|MDA]] + [[IBM 5151]], [[IBM Color Graphics Adapter|CGA]] + [[IBM 5153]], EGA, or PGA (separate adapter card)
| sound = Internal PC speaker, driven by Intel 8254 timer
| dimensions = 21.3" W × 17.3" D × 6.4" H (54 × 44 × 16 cm)
| weight = ~43 lb (19.5 kg) without keyboard or monitor
| os = IBM PC DOS 3.0 and later; OS/2 1.x; PC/IX 1.1; IBM and SCO Xenix; Windows 1.0 – 3.1
| predecessor = [[IBM PC XT (5160)|IBM PC XT]]
| successor = IBM Personal System/2 (no direct AT replacement until the IBM PS/2 Model 30 286 in 1988)
| model = 5170
}}

The '''IBM Personal Computer AT''' (model '''5170''', also known as the '''IBM AT''' or '''PC/AT''') was IBM's fourth Personal Computer, announced on August 14, 1984. It moved the IBM PC line from the 8088 to the '''Intel 80286''', introduced the '''16-bit AT bus''' (later standardised as ISA), and replaced the XT-era keyboard protocol and DIP-switch configuration with a bidirectional AT keyboard protocol and a battery-backed CMOS/RTC. The AT remained in production until early 1987 and was officially withdrawn on April 2, 1987, the day IBM announced the PS/2.

IBM never expanded the "AT" abbreviation on product packaging; it is generally taken to stand for "Advanced Technology."

== Architecture and Processor ==

The AT uses an '''Intel 80286''' CPU. Type 1 and Type 2 motherboards run at '''6 MHz''' (12 MHz crystal); the Type 3 motherboard, introduced in April 1986, runs at '''8 MHz''' (16 MHz crystal). A second socket accepts the matching '''Intel 80287''' floating-point coprocessor.

The 80286 has a 24-bit address bus that raises the addressable RAM ceiling from 1 MB (8088) to '''16 MB''', and it can operate in either real mode or '''protected mode'''.

The AT chip set on the motherboard includes:
* Two '''Intel 8259A''' programmable interrupt controllers, cascaded, providing 15 hardware IRQs.
* Two '''Intel 8237A''' DMA controllers, cascaded, providing 7 DMA channels.
* '''Intel 8254-2''' programmable interval timer (system tick, refresh trigger, speaker).
* '''Intel 82284''' clock generator and '''Intel 82288''' bus controller.
* '''Motorola MC146818''' real-time clock with 50 bytes of battery-backed CMOS RAM. Setup parameters (memory size, floppy and HDD type, etc.) are stored here in place of the DIP switches used on the 5150 and 5160.
* '''Intel 8042''' keyboard controller (an 8042-class microcontroller, also produced by IBM and others as the 8742).

The 5150/5160 cassette interface is removed entirely on the AT.

== Motherboard Revisions ==

There are three motherboard revisions, identified in IBM service documentation as Type 1, Type 2 and Type 3.

<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''IBM 5170 motherboard revisions'''
! Type !! CPU speed !! Form factor !! On-board RAM !! BIOS shipped !! Main crystal !! Submodels fitted
|-
| Type 1 || 6 MHz || 13.8" × 12" (full size AT) || 2 banks × 256 KB (stacked 41128) || 01/10/84 || 12 MHz || 5170-068, 5170-099
|-
| Type 2 || 6 MHz || 13.8" × 9.4" (Baby AT) || 1 bank × 512 KB (41256) || 06/10/85 || 12 MHz || 5170-239
|-
| Type 3 || 8 MHz || 13.8" × 9.4" (Baby AT) || 1 bank × 512 KB (41256) || 11/15/85 || 16 MHz || 5170-319, 5170-339
|}

The Type 1 motherboard can operate with only bank 0 populated (256 KB); switching between single-bank and dual-bank operation also requires the BIOS to be reconfigured via SETUP and may need jumper J18 changed.

=== BIOS revisions ===

The 5170 BIOS (including ROM BASIC) is 64 KB. On very early motherboards it shipped as four 16 KB chips (27128) in sockets U17/U27/U37/U47. Later production used two 32 KB chips (27256) in sockets U27 and U47. On Type 1 boards, shunt block U131 selects which ROM type is installed.

{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''IBM 5170 BIOS revisions'''
! Date !! Mask ROM (U27/U47) !! EPROM part numbers !! Motherboard !! Floppy support !! HDD support
|-
| 01/10/84 || U27=6181028, U47=6181029 || U17=6181024, U27=6181025, U37=6181026, U47=6181027 || Type 1 || 360 KB and 1.2 MB || 20 MB (type 1) only
|-
| 06/10/85 || U27=6480090, U47=6480091 || U27=6448896, U47=6448897 || Type 2 || 360 KB and 1.2 MB; 720 KB || 20 MB and 30 MB (type 20)
|-
| 11/15/85 || U27=62X0820, U47=62X0821 || U27=61X9266, U47=61X9265 || Type 3 || Adds 1.44 MB drive support || As above
|}

IBM officially supported an upgrade from the 01/10/84 BIOS to the 06/10/85 revision (the 30 MB hard drive upgrade kit included the 06/10/85 ROMs because the 30 MB drive required the new HDD code). The 11/15/85 BIOS is desirable for 1.44 MB floppy support but was designed for 8 MHz motherboards; running it on a 6 MHz Type 1 or Type 2 has been reported as functional by experienced users.

== Storage and Expansion ==

* '''Eight expansion slots''' on a '''16-bit AT bus''' (later standardised as ISA). The slot connector is a two-piece edge: an 8-bit XT-style portion plus a shorter 16-bit extension. Cards built for the XT (8-bit) fit in either piece, leaving the 16-bit portion unused.
* '''Floppy drive''': 1.2 MB 5.25" half-height high-density drive. The 1.2 MB drive cannot reliably write to 360 KB diskettes for later use in a 360 KB drive, because the 1.2 MB drive's head track width is half that of a 360 KB drive. The drive itself cannot detect the diskette type, so the user must use the correct media.
* '''Hard drive''': Optional 20 MB or 30 MB MFM hard drive on most submodels, connected through the '''IBM Fixed Disk and Diskette Drive Adapter''' (the "combo" controller, which combines the floppy and hard disk controllers on a single 16-bit card).
* '''Keyboard lock''': A keyed mechanical lock on the front panel disables the keyboard and holds the system unit's cover in place.

== Display ==

The AT has no on-board video. Common adapter cards used with the AT are MDA, CGA, EGA and PGA. The AT shipped most commonly with EGA from 1985 onwards.

== Keyboard ==

The AT shipped with a new '''84-key Model F AT''' keyboard. The numeric keypad is clearly separated from the main key group and three LEDs are present (Caps Lock / Scroll Lock / Num Lock). The connector is the same DIN-5 as the XT keyboard, but the electrical interface is '''bidirectional''' — the host can control the LEDs, reset the keyboard, set the typematic rate, etc. The scan code set is also different from the XT's. As a result, an XT keyboard cannot be used on an AT and vice versa without a protocol converter.

From April 1986 (Type 3 motherboard era), the AT shipped with the '''101-key Enhanced Keyboard''' (Model M).

== Power Supply ==

The 5170 includes a '''192 W switching power supply''' with two motherboard connectors (P8/P9). It requires a minimum load of '''7.0 A on +5 V''' and '''2.5 A on +12 V''' to start. Because the AT motherboard provides little +12 V load on its own, entry-level submodels that did not include a hard drive shipped with a '''5 Ω 50 W resistor''' fitted to the +12 V line of the hard drive power connector to satisfy the minimum load. The resistor draws roughly 2.4 A (about 29 W) in normal operation and gets fairly hot.

The AT serial port is built around the '''16450 UART''', which (like the 8250 in the PC/XT) has only a single-byte buffer; high-speed serial work is problematic without a 16550-equivalent replacement.

== Submodels ==

The following list of AT submodels is taken from the IBM Personal Computer Family Service Information Manual and the IBM Personal System/2 and IBM Personal Computer Publication Reference.

{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''Selected IBM PC AT submodels'''
! Submodel !! Clock !! Stock RAM !! HDD !! Notes
|-
| 5170-068 || 6 MHz || 256 KB || none || Base diskette-only configuration
|-
| 5170-099 || 6 MHz || 512 KB || 20 MB || Original "Enhanced" configuration
|-
| 5170-239 || 6 MHz || 512 KB || 30 MB || Type 2 motherboard
|-
| 5170-319 || 8 MHz || 512 KB || 30 MB || Type 3 motherboard, original Model F keyboard
|-
| 5170-339 || 8 MHz || 512 KB || 30 MB || Type 3 motherboard, ships with the Enhanced (101-key) Keyboard
|-
| 5170-839 || 6 MHz || 512 KB || two 30 MB || Includes controllers for the IBM 4680 Store System (point-of-sale)
|-
| 5170-899 || 6 MHz || 512 KB || two 20 MB || As 839 with 20 MB drives
|-
| 5170-599 / -739 / -919 / -939 || 6 MHz || 512 KB || 20 MB or 30 MB || AT/370 — System/370 host emulation board
|-
| 5171-168 / -339 || 8 MHz || 512 KB || none or 30 MB || TEMPEST-shielded variants
|}

== General Maintenance ==

PSU voltage checks, RTC battery replacement, cleaning and slot care for the AT are documented in [[IBM PC AT Maintenance Guide]].

== Troubleshooting ==

POST beep codes, 1xx system-board errors, 161/162/163 CMOS battery errors, the 601 combo-card error, CMI hard-drive symptoms and other AT-specific known problems are documented in [[IBM PC AT Troubleshooting Guide]].

== Capacitor Replacement ==

Tantalum capacitor advice for the 5170 motherboard and the AT switching PSU is documented in [[IBM PC AT Capacitor Replacement Guide]].

== Gallery ==
<gallery mode="packed" heights="200">
File:IBM PC AT 5170.jpg|IBM Personal Computer AT (5170)
File:IBM 5170 front.jpg|Front view of an IBM 5170
File:IBM 5170 back.jpg|Back view of an IBM 5170 showing keyboard, parallel, serial and video connectors
File:IBM 5170 motherboard Type 2.jpg|IBM 5170 motherboard, Type 2 (Baby AT form factor, 6 MHz)
</gallery>

== Related Pages ==

* [[IBM PC AT Maintenance Guide]]
* [[IBM PC AT Troubleshooting Guide]]
* [[IBM PC AT Capacitor Replacement Guide]]
* [[IBM PC (5150)]]
* [[IBM PC XT (5160)]] — predecessor

== References ==

* [https://en.wikipedia.org/wiki/IBM_Personal_Computer_AT IBM Personal Computer AT — Wikipedia]. Source for dimensions, release/withdrawal dates, submodel list and BIOS/keyboard history.
* [https://minuszerodegrees.net/5170/motherboard/5170_motherboard_revisions.htm IBM 5170 — Motherboard Versions], minuszerodegrees.net. Source for the Type 1/2/3 revision data, form factor, RAM type and crystal frequencies.
* [https://minuszerodegrees.net/5170/bios/5170_bios_revisions.htm IBM 5170 — BIOS Revisions], minuszerodegrees.net. Source for BIOS dates, IBM part numbers and supported floppy/HDD types.
* [https://www.dosdays.co.uk/computers/IBM%20PC-AT%20(5170)/ibm5170.php IBM PC-AT (1984) — DOS Days]. Reference for configuration and chronology.
* IBM, ''Personal Computer AT — Technical Reference'', IBM Part Numbers 1502243 (March 1984) / 1502494 / 6280070 (September 1985).

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[[Category:IBM]]