Editing IBM PS/2

{{Short description|Second generation of personal computers by IBM}}
{{Redirect|PS/2|the video game console|PlayStation 2|the keyboard and mouse connectors introduced with this system|PS/2 port|other uses|PS2 (disambiguation)}}
{{Infobox information appliance
| name = Personal System/2
| aka = PS/2
| logo = IBM PS-2 wordmark.svg
| logo_upright = 0.5
| image = Personal System 2 Series of Computers.png
| caption = An assortment of PS/2s in various form factors{{efn|From left to right: a [[IBM PS/2 Server|Server 95]], a [[IBM PS/2 Model 80|Model 80]], a [[IBM PS/2 Model 25|Model 25]], and a [[IBM PS/2 E|PS/2 E]] on top of a Model 56 and a [[IBM PS/2 Model 30 286|Model 30 286]]}}
| developer = [[IBM|International Business Machines Corporation]] (IBM)
| manufacturer = IBM
| type = Personal computers
| releasedate = {{Start date and age|1987|04|02}}
| discontinued = July 1995
| media = {{hlist|3.5-inch [[floppy disk]]s|5.25-inch floppy disks {{small|(optional, external drive)}}}}
| os = {{hlist|[[IBM PC DOS]]|[[OS/2]]|[[Windows 2.0x]]|[[Windows 3.0]]|[[Windows 3.1x]]|[[Windows NT 3.1]]|[[Windows NT 3.5]]}}
| power = 120/240 VAC {{polarity|ac}} {{small|(desktops)}}
| cpu = Various; see [[List of IBM PS/2 models|list of models]]
| graphics = [[VGA]]
| predecessor = [[IBM Personal Computer AT|Personal Computer AT]]
| successor = {{ubl|[[IBM PS/ValuePoint|PS/ValuePoint]] and [[IBM PC Series#PC Series 700|PC Series 700]] {{small|(desktops)}}|[[ThinkPad]] {{small|(portables)}}}}
| related = {{hlist|[[IBM PS/1|PS/1]]|[[Ambra Computer Corporation|Ambra]]}}
}}

The '''Personal System/2''' or '''PS/2''' is [[IBM]]'s second generation<ref>{{cite book | last=Tooley | first=Mike | date=1995 | url=https://books.google.com/books?id=QX_NCgAAQBAJ | title=PC-based Instrumentation and Control | publisher=Elsevier | page=19 | isbn=9780080938271 | via=Google Books | access-date=2023-03-21 | archive-date=2023-04-25 | archive-url=https://web.archive.org/web/20230425164211/https://books.google.com/books?id=QX_NCgAAQBAJ | url-status=live }}</ref><ref>{{cite web | last=Clancy | first=Heather | date=June 2, 1988 | url=https://www.upi.com/Archives/1988/06/02/IBM-adds-to-second-generation-of-personal-computers/7134581227200/ | title=IBM adds to second generation of personal computers | publisher=UPI | page=219 | access-date=February 21, 2022 | archive-date=February 21, 2022 | archive-url=https://web.archive.org/web/20220221030516/https://www.upi.com/Archives/1988/06/02/IBM-adds-to-second-generation-of-personal-computers/7134581227200/ | url-status=live }}</ref> of [[personal computer]]s. Released in 1987, it officially replaced the [[IBM Personal Computer|IBM PC]], [[IBM Personal Computer XT|XT]], [[IBM Personal Computer/AT|AT]], and [[IBM PC Convertible|PC Convertible]] in IBM's lineup. Many of the PS/2's innovations, such as the [[16550 UART]] (serial port), 1440 KB 3.5-inch [[floppy disk]] format, 72-pin [[SIMM]]s, [[#Keyboard/mouse|PS/2 port]], and [[#Graphics|VGA video standard]], went on to become standards in the broader PC market.<ref>{{cite book |author=<!--Staff writer(s); no by-line.--> |url=http://www.nj7p.org/Computers/IBM%20PC/work/PS2_HI.pdf |title=IBM Personal System/2 Hardware Interface Technical Reference |publisher=IBM |date=May 1988 |id=68X2330 |access-date=2016-11-26 |archive-date=2020-10-29 |archive-url=https://web.archive.org/web/20201029050152/http://www.nj7p.org/Computers/IBM%20PC/work/PS2_HI.pdf |url-status=dead }}</ref><ref>{{cite web |url=http://www.mcamafia.de/pdf/pdfref.htm |title=PS/2 Reference Manuals |date=2006-03-04 |website=MCA Mafia |access-date=2016-11-26 |archive-date=2016-11-03 |archive-url=https://web.archive.org/web/20161103035051/http://www.mcamafia.de/pdf/pdfref.htm |url-status=live }}</ref>

The PS/2 line was created by IBM partly in an attempt to recapture control of the PC market by introducing the advanced yet [[Vendor lock-in|proprietary]] [[Micro Channel architecture]] (MCA) on higher-end models. These models were in the strange position of being incompatible with the hardware standards previously established by IBM and adopted in the [[IBM PC compatible]] industry. Most major PC manufacturers balked at IBM's licensing terms for MCA-compatible hardware, particularly the per-machine royalties. The [[OS/2]] operating system was announced at the same time as the PS/2 line and was intended to be the primary operating system for models with [[Intel 80286]] or later processors. However, at the time of the first shipments, only [[IBM PC DOS]] 3.3 was available. OS/2 1.0 (text-mode only) and Microsoft's [[Windows 2.0]] became available several months later. IBM also released [[IBM AIX|AIX]] PS/2, a [[Unix|UNIX]] operating system for PS/2 models with [[Intel 80386|Intel 386]] or later processors.

IBM's initial PS/2 computers were popular with target market corporate buyers, and by September 1988, IBM reported that it had sold 3 million PS/2 machines in the past 18 months. However, the PS/2 was unsuccessful in the consumer market since IBM failed to establish a link in the consumer's mind between the PS/2 MicroChannel architecture and the immature OS/2 1.x operating system (the more capable OS/2 version 2.0 was not released until 1992) to justify the PS/2's price premium, in contrast to rival [[IBM PC compatible]]s that stuck with industry-wide standard hardware while running [[Microsoft Windows]].<ref>{{cite magazine|url=https://techland.time.com/2012/04/02/25-years-of-ibms-os2-the-birth-death-and-afterlife-of-a-legendary-operating-system/2/|title=25 Years of IBM's OS/2: The Strange Days and Surprising Afterlife of a Legendary Operating System|first=Harry|last=McCracken|magazine=Time|date=2 April 2012|via=techland.time.com|access-date=29 September 2015|archive-date=30 September 2015|archive-url=https://web.archive.org/web/20150930084010/http://techland.time.com/2012/04/02/25-years-of-ibms-os2-the-birth-death-and-afterlife-of-a-legendary-operating-system/2/|url-status=live}}</ref> Rival manufacturers also teamed up to form the [[Extended Industry Standard Architecture|EISA]] bus standard in opposition to the Micro Channel.<ref>{{cite web | url=https://www.nytimes.com/1989/02/09/business/ibm-and-rebels-head-for-battle.html | title=I.B.M. And Rebels Head for Battle | work=The New York Times | date=9 February 1989 | last1=Markoff | first1=John }}</ref> In 1992, ''[[Macworld]]'' stated that "IBM lost control of its own market and became a minor player with its own technology."<ref name="borrell199205">{{Cite magazine|last=Borrell|first=Jerry|date=May 1992|title=Opening Pandora's Box|url=https://archive.org/stream/MacWorld_9205_May_1992#page/n21/mode/2up|magazine=Macworld|pages=21–22}}</ref> IBM officially retired the PS/2 line in July 1995.<ref name="discontinued">{{cite journal |last1=Singh |first1=Jai |title=MCA, PS/2 bite the dust; OS/2 to follow? |journal=InfoWorld |date=April 10, 1995 |volume=17 |issue=15 |page=3 |url=https://books.google.com/books?id=oToEAAAAMBAJ&pg=PA3 |access-date=August 17, 2021 |archive-date=November 9, 2023 |archive-url=https://web.archive.org/web/20231109224853/https://books.google.com/books?id=oToEAAAAMBAJ&pg=PA3#v=onepage&q&f=false |url-status=live }}</ref>

==Technology==
{| class="wikitable" style="float:right;clear:both;"
|+Predecessors to the PS/2
|-
! Name !! Year
|-
| [[IBM Personal Computer]] || 1981
|-
| [[IBM Personal Computer XT]] || 1983
|-
| [[IBM Portable Personal Computer]] || 1984
|-
| [[IBM PCjr]] || 1984
|-
| [[IBM Personal Computer/AT]] || 1984
|-
| [[IBM PC Convertible]] || 1986
|-
| [[IBM Personal Computer XT#IBM XT 286|IBM Personal Computer XT 286]] || 1986
|}
IBM's PS/2 was designed to remain software compatible with their PC/AT/XT line of computers upon which the large [[IBM PC compatible|PC clone]] market was built, but the hardware was quite different. PS/2 had two [[BIOS]]es: one named ABIOS (Advanced BIOS) which provided a new [[protected mode]] interface and was used by OS/2, and CBIOS (Compatible BIOS) which was included to be software compatible with the PC/XT/AT. CBIOS was so compatible that it even included [[Cassette BASIC]]. While IBM did not publish the BIOS source code, it did promise to publish BIOS [[entry point]]s.{{r|byte198706}}

===Micro Channel architecture===
{{main|Micro Channel architecture}}
With certain models to the IBM PS/2 line, [[Micro Channel architecture|Micro Channel Architecture]] (MCA) was also introduced.{{r|byte198706}} MCA was conceptually similar to the channel architecture of the [[IBM System/360]] mainframes. MCA was technically superior to [[Industry Standard Architecture|ISA]] and allowed for higher-speed communications within the system. The majority of MCA's features would be seen in later buses with the exception of: streaming-data procedure, channel-check reporting, error logging<ref>{{cite web|url=http://www.mcamafia.de/pdf/server_hmm_s30h2501_01.pdf|access-date=30 April 2023|title=Hardware Maintenance Manual|date=March 1996|website=mcamafia.de|archive-date=25 April 2023|archive-url=https://web.archive.org/web/20230425135058/http://www.mcamafia.de/pdf/server_hmm_s30h2501_01.pdf|url-status=live}}</ref> and internal bus-level video pass-through for devices like the [[IBM 8514]]. Transfer speeds were on par with the much later [[Peripheral Component Interconnect|PCI]] standard. MCA allowed one-to-one, card-to-card, and multi-card to processor simultaneous transaction management which is a feature of the [[PCI-X]] bus format.

Bus mastering capability, bus arbitration, and a primitive form of [[plug and play|plug-and-play]] management of hardware were all benefits of MCA. Gilbert Held in his 2000 book ''Server Management'' observes: "MCA used an early (and user-hostile) version of what we know now as 'Plug-N′-Play', requiring a special setup disk for each machine and each card."<ref name="Held2000">{{cite book|author=Gilbert Held|title=Server Management|url=https://books.google.com/books?id=Y9q-i_HGtAAC&pg=PA199|year=2000|publisher=CRC Press|isbn=978-1-4200-3106-5|page=199}}</ref> MCA never gained wide acceptance outside of the PS/2.

When setting up the card with its disk, all choices for interrupts and other changes were accomplished automatically by the PC reading the old configuration from the floppy disk. This made necessary changes, then recorded the new configuration to the floppy disk. This meant that the user must keep that same floppy disk matched to that particular PC. For a small organization with a few PCs, this was annoying, but less expensive and time-consuming than bringing in a PC technician to do installation. But for large organizations with hundreds or even thousands of PCs, permanently matching each PC with its own floppy disk was a logistical nightmare. Without the original, (and correctly updated) floppy disk, no changes could be made to the PC's cards.

===Keyboard/mouse===

====Layout====
The PS/2 IBM [[Model M keyboard]] used the same 101-key layout of the previous [[IBM PC/AT]] Extended keyboard.{{r|byte198706}}  European variants had 102 keys with the addition of an extra key to the right of the left Shift key.

====Interface====
{{further|PS/2 port}}
[[Image:IBM PS2 hiiri.jpg|upright|thumb|left|The original IBM PS/2 mouse]]
[[Image:ps-2-ports.jpg|thumb|right|PS/2 connection ports (later colored purple for keyboard and green for mouse, according to [[PC 97]]) were once commonly used for connecting input devices.]]

PS/2 systems introduced a new specification for the [[Computer keyboard|keyboard]] and [[computer mouse|mouse]] interfaces, which are still in use today{{Citation needed|date=March 2025|reason=This might have been true a decade ago, but practically no new peripherals uses these interfaces, and very little (newly manufactured) computer hardware even has the physical connectors.}} (though increasingly supplanted by [[USB]] devices) and are thus called "PS/2" interfaces. The PS/2 keyboard interface, inspired by Apple's ADB interface, was electronically identical to the long-established [[AT Keyboard|AT]] interface, but the cable connector was changed from the 5-pin [[DIN connector]] to the smaller 6-pin [[Mini-DIN connector|mini-DIN]] interface. The same connector and a similar synchronous serial interface was used for the PS/2 mouse port.

The initial desktop ''[[IBM PS/2 Model 50|Model 50]]'' and ''[[IBM PS/2 Model 60|Model 60]]'' also featured a new cableless internal design, based on use of interposer circuit boards to link the internal drives to the planar (motherboard). Additionally, these machines could be largely disassembled and reassembled for service without tools.

Additionally, the PS/2 introduced a new software data area known as the [[Extended BIOS Data Area]] (EBDA). Its primary use was to add a new buffer area for the dedicated mouse port. This also required making a change to the "traditional" [[BIOS Data Area]] (BDA) which was then required to point to the base address of the EBDA.

Another new PS/2 innovation was the introduction of bidirectional [[parallel port]]s which, in addition to their traditional use for connecting a printer, could now function as a high-speed data transfer interface. This allowed the use of new hardware such as parallel port [[Image scanner|scanner]]s, CD-ROM drives, and also enhanced the capabilities of printers by allowing them to communicate with the host PC and send back signals instead of simply being a passive output device.

===Graphics===
Most of the initial range of PS/2 models were equipped with a new [[frame buffer]] known as the [[Video Graphics Array]], or VGA for short. This effectively replaced the previous [[Enhanced Graphics Adapter|EGA]] standard.{{r|byte198706}} VGA increased graphics memory to 256&nbsp;KB and provided for resolutions of 640×480 with 16 colors, and {{resx|320×200}} with 256 colors. VGA also provided a palette of [[List of monochrome and RGB color formats#18-bit RGB|262,144 colors]] (as opposed to the EGA palette of 64 colors). The [[IBM 8514]] and later [[Extended Graphics Array|XGA]] [[computer display standard]]s were also introduced on the PS/2 line.

Key monitors and their maximum resolutions:
*8504: 12-inch, {{resx|640×480}}, 60&nbsp;Hz [[non-interlaced]], 1991, monochrome
*8507: 19-inch, {{resx|1024×768}}, 43.5&nbsp;Hz [[interlaced]], 1988, monochrome
*8511: 14-inch, {{resx|640×480}}, 60&nbsp;Hz [[non-interlaced]], 1987
*8512: 14-inch, {{resx|640×480}}, 60&nbsp;Hz [[non-interlaced]], 1987
*8513: 12-inch, {{resx|640×480}}, 60&nbsp;Hz [[non-interlaced]], 1987
*8514: 16-inch, {{resx|1024×768}}, 43.5&nbsp;Hz [[interlaced]], 1987
*8515: 14-inch, {{resx|1024×768}}, 43.5&nbsp;Hz [[interlaced]], 1991
*8516: 14-inch, {{resx|1024×768}}, 43.5&nbsp;Hz [[interlaced]], 1991
*8518: 14-inch, {{resx|640×480}}, 75&nbsp;Hz [[non-interlaced]], 1992
*9515: 14-inch, {{resx|1024×768}}, 43.5&nbsp;Hz [[interlaced]], 1992
*9517: 16-inch, {{resx|1280×1024}}, 53&nbsp;Hz [[interlaced]], 1991
*9518: 14-inch, {{resx|640×480}}, [[non-interlaced]], 1992
*38F4737: 10-inch, {{resx|640×480}}, [[non-interlaced]], 1989, amber monochrome plasma screen; this display was exclusive to models P70 and P75

In truth, all XGA {{resx|1024×768}} monitors are multimode, as XGA works as an add-on card to a built-in VGA and transparently passes the VGA signal through when not operating in a high-resolution mode. All of the listed 85xx displays can therefore sync 640×480 at 60&nbsp;Hz (or {{resx|720×400}} at 70&nbsp;Hz) in addition to any higher mode they may also be capable of. This however is not true of the 95xx models (and some unlisted 85xx's), which are specialist workstation displays designed for use with the XGA-2 or Image Adapter/A cards, and whose fixed frequencies all exceed that of basic VGA – the lowest of their commonly available modes instead being {{resx|640×480}} at 75&nbsp;Hz, if not something much higher still. It is also worth noting that these were still merely dual- or "multiple-frequency" monitors, not variable-frequency (also known as multisync); in particular, despite running happily at {{resx|640×480}}, {{resx|720×400}} and {{resx|1024×768}}, an (e.g.) 8514 cannot sync the otherwise common intermediate {{resx|800×600}} SVGA resolution, even at the relatively low 50 to 56&nbsp;Hz refresh rates initially used.

Although the design of these adapters did not become an industry standard as VGA did, their {{resx|1024×768}} pixel resolution was subsequently widely adopted as a standard by other manufacturers, and XGA became a synonym for this screen resolution. The only exceptions were the bottom-rung 8086-based Model 25 and 30, which had a cut-down version of VGA referred to as [[Multi-Color Graphics Array|MCGA]]; the 286 models came with VGA. This supported CGA graphics modes, VGA {{resx|320×200}} 256 color and {{resx|640×480}} monochrome mode, but not EGA or color {{resx|640×480}}.

[[File:MCA IBM XGA-2.jpg|thumb|MCA IBM XGA-2 graphics card]]

====VGA video connector====
All of the new PS/2 graphics systems (whether MCGA, VGA, 8514, or later XGA) used a 15-pin [[D-sub]] connector for video out. This used analog RGB signals, rather than four or six digital color signals as on previous CGA and EGA monitors. The digital signals limited the color gamut to a fixed 16- or 64-color palette with no room for expansion.  In contrast, any color depth (bits per primary) can be encoded into the analog RGB signals so the color gamut can be increased arbitrarily by using wider (more bits per sample) [[digital-to-analog converter|DACs]] and a more sensitive monitor. The connector was also compatible with analog grayscale displays. Unlike earlier systems such as [[IBM Monochrome Display Adapter|MDA]] and [[Hercules Graphics Card|Hercules]], this was transparent to software, so all programs supporting the new standards could run unmodified whichever type of display was attached. On the other hand, whether the display was color or monochrome was undetectable to software, so selection between application displays optimized for color or monochrome, in applications that supported both, required user intervention. These grayscale displays were relatively inexpensive during the first few years the PS/2 was available, and they were very commonly purchased with lower-end models.

The [[VGA connector]] became the de facto standard for connecting monitors and projectors on both PC and non-PC hardware over the course of the early 1990s, replacing a variety of earlier connectors.

===Storage===
[[File:IBM PS2 MCA Model 70, riser for floppy and hard drive.jpg|thumb|Some PS/2 models used a quick-attachment socket on the back of the floppy drive which is incompatible with a standard 5.25-inch floppy connector.]]
[[Image:IBM PS2 MCA Model 55 SX, hard drive bus closeup.jpg|thumb|left|Close-up of unusual 72-pin MCA internal hard drive connector]]

Apple had first popularized the 3.5-inch floppy on the Macintosh line and IBM brought them to the PC in 1986 with the [[PC Convertible]]. In addition, they could be had as an optional feature on the XT and AT. The PS/2 line used entirely 3.5-inch drives which assisted in their quick adoption by the industry, although the lack of 5.25-inch drive bays in the computers created problems later on in the 1990s as they could not accommodate internal CD-ROM drives. In addition, the lack of built-in 5.25-inch floppy drives meant that PS/2 users could not immediately run the large body of existing IBM-compatible software.<ref>{{cite web |url=http://www.disktrend.com/pdf/portrpkg.pdf |archive-url=https://web.archive.org/web/20120328044723/http://www.disktrend.com/pdf/portrpkg.pdf |title=100th Anniversary Conference: Magnetic Recording and Information Storage |date=1998-12-14 |access-date=2014-03-24 |archive-date=2012-03-28 |author=Jim Porter |publisher=disktrend.com}}</ref> However IBM made available optional external 5.25-inch drives, with internal adapters for the early PS/2 models, to enable data transfer.
[[File:IBM 3.5-inch DD and HD diskettes.jpg|thumb|3.5-inch DD and HD floppies]]
In the initial lineup, IBM used 720&nbsp;KB double density (DD) capacity drives on the 8086-based models and 1440&nbsp;KB high density (HD) on the 80286-based and higher models. By the end of the PS/2 line they had moved to a somewhat standardized capacity of 2880&nbsp;KB.

The PS/2 floppy drives lacked a capacity detector. 1440&nbsp;KB floppies had a hole so that drives could distinguish them from 720&nbsp;KB floppies, preventing users from formatting the smaller capacity disks to the higher capacity (doing so would work, but with a higher tendency of data loss). Clone manufacturers implemented the hole detection, but IBM did not. As a result of this a 720 KB floppy could be formatted to 1440&nbsp;KB in a PS/2, but the resulting floppy would only be readable by a PS/2 machine.<ref>{{cite web|url=http://ohlandl.ipv7.net/floppy/floppy.html#Format_720K_On_144MB|title=floppy|first=Louis|last=Ohland|website=ohlandl.ipv7.net|access-date=2011-02-19|archive-date=2011-07-23|archive-url=https://web.archive.org/web/20110723160004/http://ohlandl.ipv7.net/floppy/floppy.html#Format_720K_On_144MB|url-status=live}}</ref>

PS/2s primarily used [[Mitsubishi]] floppy drives and did not use a separate Molex power connector; the data cable also contained the power supply lines. As the hardware aged the drives often malfunctioned due to bad quality [[capacitor]]s.{{Citation needed|date=February 2019}}

The PS/2 used several different types of internal hard drives. Early models used [[Modified Frequency Modulation|MFM]] or [[Enhanced Small Disk Interface|ESDI]] drives. Some desktop models used combo power/data cables similar to the floppy drives. Later models used [[DBA ESDI]] or [[Parallel SCSI]]. Typically, desktop PS/2 models only permitted use of one hard drive inside the computer case. Additional storage could be attached externally using the optional SCSI interface.

===Memory===
Later PS/2 models introduced the [[SIMM#72-pin SIMMs|72-pin SIMM]]<ref>{{Cite news|url=https://www.pcworld.com/article/258989/the_ibm_ps_2_25_years_of_pc_history.html|title=The IBM PS/2: 25 Years of PC History|work=PCWorld|access-date=2018-08-28|language=en|archive-date=2018-10-04|archive-url=https://web.archive.org/web/20181004213847/https://www.pcworld.com/article/258989/the_ibm_ps_2_25_years_of_pc_history.html|url-status=live}}</ref> which became the [[de facto]] standard for [[Random-access memory|RAM]] modules by the mid-1990s in mid-to-late [[i486|486]] and nearly all [[Pentium (original)|Pentium]] desktop systems. The 72-pin SIMMs were 32/36 bits wide and replaced the old [[SIMM#30-pin SIMMs|30-pin SIMM]] (8/9-bit) standard. The older SIMMs were much less convenient because they had to be installed in sets of two or four to match the width of the CPU's 16-bit (Intel 80286 and [[i386#The 80386SX variant|80386SX]]) or 32-bit (80386 and [[i486|80486]]) data bus, and would have been extremely inconvenient to use in Pentium systems (which featured a 64-bit memory bus). The 72-pin SIMMs were also made with greater capacities (starting at 1 MB and ultimately reaching 128 MB, instead of 256 KB to 16 MB (and usually no more than 4 MB) for 30-pin) and in a more finely graduated range (powers of 2, instead of powers of 4).

Many PS/2 models also used proprietary IBM SIMMs and could not be fitted with commonly available types. However industry standard SIMMs could be modified to work in PS/2 machines if the SIMM-presence and SIMM-type detection bridges, or associated contacts, were correctly rewired.{{Citation needed|date=November 2021}}

==Models==
{{Main|List of IBM PS/2 models}}
At launch, the PS/2 family comprised the [[IBM PS/2 Model 30|Model 30]], [[IBM PS/2 Model 50|50]], [[IBM PS/2 Model 60|60]] and [[IBM PS/2 Model 80|80]];{{r|byte198706}} the [[IBM PS/2 Model 25|Model 25]] was launched a few months later.
[[File:IBM Personal System2 Intel 286 computer.ogg|thumb|IBM Personal System/2 [[IBM PS/2 Model 30 286|Model 30 286]]. [[Power-on self-test]], [[bootstrapping (computing)|bootstrapping]], power-off]]
The PS/2 Models 25 and 30 (IBM 8525 and 8530, respectively) were the lowest-end models in the lineup and meant to replace the IBM PC and XT. Model 25s came with either an 8086 CPU running at 8&nbsp;MHz, 512&nbsp;KB of RAM, and 720&nbsp;KB floppy disks, or 80286 CPU. The 8086s had ISA expansion slots and a built-in MCGA monitor, which could be either color or monochrome, while the 80286 models came with VGA monitor and ISA expansion slots. A cut-down Model M keyboard with no numeric keypad was standard, with the normal keyboard being an extra-cost option. There was a very rare later model called the PS/2 Model 25-SX which sported either a 16&nbsp;MHz or 20&nbsp;MHz 386 CPU, up to 12&nbsp;MB of memory, IDE hard drive, VGA Monitor and 16&nbsp;bit ISA slots making it the highest available model 25 available denoted by model number 8525-L41.

[[File:25-sx.jpg|thumb|Case badge on a [[IBM PS/2 Model 25|Model 25 SX]] (8525-L41)]] The Model 30 had either an 8086 or 286 CPU and sported the full 101-key keyboard and standalone monitor along with three 8-bit ISA expansion slots. 8086 models had 720&nbsp;KB floppies while 286 models had 1440&nbsp;KB ones. Both the Model 25 and 30 could have an optional 20&nbsp;MB [[ST-506]] hard disk (which in the Model 25 took the place of the second floppy drive if so equipped and used a proprietary 3.5" form factor). 286-based Model 30s are otherwise a full AT-class machine and support up to 4&nbsp;MB of RAM.

[[File:Personal System 2 Model 25.png|thumb|upright|IBM Personal System/2 [[IBM PS/2 Model 25|Model 25]]]]
Later ISA PS/2 models comprised the [[IBM PS/2 Model 30|Model 30 286]] (a Model 30 with an [[Intel 286]] CPU), ''Model 35'' (IBM 8535) and ''Model 40'' (IBM 8540) with [[Intel 80386|Intel 386SX]] or IBM [[386SLC]] processors.

The higher-numbered models (above 50) were equipped with the Micro Channel bus and mostly [[Enhanced Small Disk Interface|ESDI]] or [[SCSI]] [[hard drive]]s (models 60-041 and 80-041 had [[Modified Frequency Modulation|MFM]] hard drives). PS/2 ''Models 50'' (IBM 8550) and ''60'' (IBM 8560) used the [[Intel 80286|Intel 286]] processor, the PS/2 ''[[IBM PS/2 Model 70|Models 70 386]]'' (IBM 8570) and ''80'' used the [[Intel 80386|386DX]], while the mid-range PS/2 ''[[IBM PS/2 Model 55 SX|Model 55 SX]]'' (IBM 8555–081) and used the 16/32-bit 386SX processor. The ''Model 50'' was revised to the ''[[IBM PS/2 Model 50 Z|Model 50 Z]]'' still with 10&nbsp;MHz 80286 processor, but with memory run at zero wait state, and a switch to ESDI hard drives. Later [[IBM PS/2 Model 70 486|Model 70 486]] and 80 variants (B-xx) also used 25&nbsp;MHz [[Intel 80486|Intel 486]] processors, in a complex called the Power Platform.

[[File:DeuxPS2.jpg|thumb|upright|The externally very similar [[IBM PS/2 Model 60|Models 60]] and [[IBM PS/2 Model 80|80]] next to each other]]
[[File:IBM Model70 80386.JPG|thumb|IBM Model 70 (case open over case closed)]]
The PS/2 ''Models 90'' (IBM 8590/9590) and ''95'' (IBM 8595/9595/9595A) used Processor Complex [[daughterboard]]s holding the [[Central processing unit|CPU]], memory controller, MCA interface, and other system components.  The available Processor Complex options ranged from the 20&nbsp;MHz [[Intel 80486|Intel 486]] to the 90&nbsp;MHz [[Intel P5|Pentium]] and were fully interchangeable. The IBM ''PC Server 500'', which has a motherboard identical to the 9595A, also uses Processor Complexes.

Other later Micro Channel PS/2 models included the Model ''65SX'' with a 16&nbsp;MHz 386SX; various ''Model 53'' (IBM 9553), ''56'' (IBM 8556) and ''57'' (IBM 8557) variants with 386SX, 386SLC or 486SLC2 processors; the ''Models 76'' and ''77'' (IBM 9576/9577) with 486SX or 486DX2 processors respectively; and the 486-based ''Model 85'' (IBM 9585).

The IBM ''[[PS/2E]]'' (IBM 9533) was the first [[Energy Star]] compliant personal computer. It had a 50&nbsp;MHz [[IBM 486SLC]] processor, an [[Industry Standard Architecture|ISA]] bus, four [[PC card]] slots, and an [[Advanced Technology Attachment|IDE]] hard drive interface.  The environmentally friendly PC borrowed many components from the [[ThinkPad]] line and was composed of recycled plastics, designed to be easily recycled at the end of its life, and used very little power.

The IBM PS/2 '''''Server''' 195'' and ''295'' (IBM 8600) were 486-based dual-bus MCA network [[server computer|server]]s supporting [[asymmetric multiprocessing]], designed by [[Parallan Computer|Parallan Computer Inc]].

The IBM ''PC Server 720'' (IBM 8642) was the largest MCA-based server made by IBM, although it was not, strictly speaking, a PS/2 model. It could be fitted with up to six Intel Pentium processors interconnected by the [[Corollary C-bus]] and up to eighteen SCSI hard disks. This model was equipped with seven combination MCA/[[Peripheral Component Interconnect|PCI]] slots.

=== PS/2 portables, laptops and notebooks ===
{{Main|IBM PS/2 portable computers|IBM PS/2 Note and PS/note}}[[File:IBM PS2 N33.jpg|thumb|PS/2 N33SX laptop (1992)]]
IBM also produced several '''portable and [[laptop]] PS/2s''', including the ''[[IBM PS/2 Model L40 SX|Model L40]]'' (ISA-bus 386SX), ''N33'' (IBM's first notebook-format computer from year 1991, Model 8533, 386SX), ''N51'' (386SX/SLC), ''P70'' (386DX) and ''P75'' (486DX2).

The IBM ''ThinkPad 700C'', aside from being labeled "700C PS/2" on the case, featured MCA and a 486SLC CPU.

===6152 Academic System===
{{See also|IBM ROMP|IBM RT PC}}
The 6152 Academic System was a [[Workstation|workstation computer]] developed by IBM's Academic Information Systems (ACIS) division for the university market introduced in February 1988. The 6152 was based on the PS/2 Model 60, adding a RISC Adapter Card on the [[Micro Channel]] bus. This card was a co-processor that enabled the 6152 to run [[IBM ROMP|ROMP]] software compiled for IBM's [[Academic Operating System]] (AOS), a version of [[BSD UNIX]] for the ROMP that was only available to select colleges and universities.<ref>{{cite magazine |last=LaPlante |first=Alice |date=1988-02-08 |title=Workstation Merges PS/2, RT Technology |magazine=InfoWorld |volume=10 |issue=6 |pages=1, 81}}</ref>

The RISC Adapter Card contained the ROMP-C microprocessor (an enhanced version of the ROMP that first appeared in the [[IBM RT PC]] workstations), a [[memory management unit]] (the ROMP had [[virtual memory]]), a [[Floating-point unit|floating-point]] [[coprocessor]], and up to 8{{nbsp}}MB of memory for use by the ROMP.<ref>{{cite book |author=<!--Staff writer(s)--> |title=IBM Academic System 6152: Quick Reference and Reference Diskette |date=January 1988 |page=2}}</ref> The 6152 was the first computer to use the ROMP-C, which would later be introduced in new RT PC models.<ref>{{cite magazine |author=The University of Michigan Computing Center |year=c. 1988 |title=UNIX Notes |magazine=U-M Computing News |volume=3 |page=19}}</ref>

==Marketing==
[[File:IBM PS 2 in use - late 1980s.jpg|right|thumb|An IBM PS/2 in use in an office, probably late 1980s]]
During the 1980s, IBM's advertising of the [[IBM Personal Computer|original PC]] and its other product lines had frequently used the likeness of [[Charlie Chaplin]].

Another campaign featured actors from the television show ''[[M*A*S*H (TV series)|M*A*S*H]]'' playing the staff of a contemporary (i.e. late-1980s) business in roles reminiscent of their characters' roles from the series. Harry Morgan, Larry Linville, William Christopher, Wayne Rogers, Gary Burghoff, Jamie Farr, and Loretta Swit were in from the beginning, whereas Alan Alda joined the campaign later.<ref>{{cite web|title=M*A*S*H Cast Commercials - IMB PS/2|website = [[YouTube]]|url=https://www.youtube.com/watch?v=f7Dqe4GQtjI| archive-url=https://web.archive.org/web/20150528034318/https://www.youtube.com/watch?v=f7Dqe4GQtjI| archive-date=2015-05-28 | url-status=dead|access-date=13 April 2014}}</ref>

The profound lack of success of these advertising campaigns led, in part, to IBM's termination of its relationships with its global [[advertising agency|advertising agencies]]; these accounts were reported by [[Wired (magazine)|''Wired'']] magazine to have been worth over $500 million a year, and the largest such account review in the history of business.<ref name="Advert">''Wired'', Issue 3.08, August 1995</ref>

==Sales==
Overall, the PS/2 line was largely unsuccessful with the consumer market, even though the PC-based Models 30 and 25 were an attempt to address that.  With what was widely seen as a technically competent but [[Cynicism (contemporary)|cynical]] attempt to gain undisputed control of the market, IBM unleashed an industry backlash, which went on to standardize VESA, EISA and PCI. In large part, IBM failed to establish a link in the consumer's mind between the PS/2 MicroChannel architecture and the immature OS/2 1.x operating system; the more capable OS/2 version 2.0 was not released until 1992.<ref>{{cite magazine|url=https://techland.time.com/2012/04/02/25-years-of-ibms-os2-the-birth-death-and-afterlife-of-a-legendary-operating-system/2/|title=25 Years of IBM's OS/2: The Strange Days and Surprising Afterlife of a Legendary Operating System|first=Harry|last=McCracken|magazine=Time|date=2 April 2012|via=techland.time.com|access-date=29 September 2015|archive-date=30 September 2015|archive-url=https://web.archive.org/web/20150930084010/http://techland.time.com/2012/04/02/25-years-of-ibms-os2-the-birth-death-and-afterlife-of-a-legendary-operating-system/2/|url-status=live}}</ref>

The firm suffered massive financial losses for the remainder of the 1980s, forfeiting its previously unquestioned position as the industry leader, and eventually lost its status as the largest manufacturer of personal computers, first to [[Compaq]] and then to [[Dell]]. From a high of 10,000 employees in Boca Raton before the PS/2 came out, only seven years later, IBM had $600 million in unsold inventory and was laying off staff by the thousands.<ref>{{Cite web|url=http://www.bocahistory.org/our-history-ibm/|title=IBM in Boca Raton &#124; First Personal Computer &#124; Companies in Boca Raton|access-date=2017-11-03|archive-date=2017-11-07|archive-url=https://web.archive.org/web/20171107023344/http://www.bocahistory.org/our-history-ibm/|url-status=dead}}</ref><ref>{{Cite news |last=Vijayan |first=Jaikumar |date=August 1, 1994 |title=IBM cuts PC force, kills Ambra Corp. |volume=28 |pages=4 |work=Computerworld |issue=31 |url=https://books.google.com/books?id=mEU4Qex5594C&pg=PA4 |access-date=August 7, 2022 |archive-date=November 9, 2023 |archive-url=https://web.archive.org/web/20231109224854/https://books.google.com/books?id=mEU4Qex5594C&pg=PA4#v=onepage&q&f=false |url-status=live }}</ref> 
After the failure of the PS/2 line to establish a new standard, IBM was forced to revert to building ISA PCs&mdash;following the industry it had once led&mdash;with the low-end [[IBM PS/1|PS/1]] line and later with the more compatible [[IBM Aptiva|Aptiva]] and [[IBM PS/ValuePoint|PS/ValuePoint]] lines.

Still, the PS/2 platform experienced some success in the corporate sector where the reliability, ease of maintenance and strong corporate support from IBM offset the rather daunting cost of the machines. Also, many people still lived with the motto "[[Nobody ever got fired for buying an IBM]]". In the mid-range desktop market, the models 55SX and later 56SX were the leading sellers for almost their entire lifetimes.{{citation needed|date=December 2022}} Later PS/2 models saw a production life span that took them into the late 1990s, within a few years of IBM selling off the division.

== Timeline ==
{{Timeline of the IBM Personal Computer}}

== Notes ==
{{notelist}}

== References ==
{{Reflist|refs=
<ref name="byte198706">{{cite news | url=https://archive.org/stream/byte-magazine-1987-06/1987_06_BYTE_12-06_CAD_Mice_12-MHz_ATs_IBM_PS2_Family#page/n131/mode/2up | title=The IBM PS/2 Computers | work=BYTE | date=June 1987 | access-date=5 November 2013 | author=BYTE editorial staff | pages=100}}</ref>
}}

=== Further reading ===
* Burton, Greg. ''IBM PC and PS/2 pocket reference''. NDD (the old dealer channel), 1991.
* Byers, T.J. ''IBM PS/2: A Reference Guide''. Intertext Publications, 1989. {{ISBN|0-07-009525-6}}.
* Dalton, Richard and Mueller, Scott. ''IBM PS/2 Handbook ''. Que Publications, 1989. {{ISBN|0-88022-334-0}}.
* Held, Gilbert. ''IBM PS/2: User's Reference Manual''. John Wiley & Sons Inc., 1989. {{ISBN|0-471-62150-1}}.
* Hoskins, Jim. ''IBM PS/2''. John Wiley & Sons Inc., fifth revised edition, 1992. {{ISBN|0-471-55195-3}}.
* Leghart, Paul M. ''The IBM PS/2 in-depth report''. Pachogue, NY: Computer Technology Research Corporation, 1988.
* Newcom, Kerry. ''A Closer Look at IBM PS/2 Microchannel Architecture''. New York: McGraw-Hill, 1988.
* Norton, Peter. ''Inside the IBM PC and PS/2''. Brady Publishing, fourth edition 1991. {{ISBN|0-13-465634-2}}.
* ''Outside the IBM PC and PS/2: Access to New Technology''. Brady Publishing, 1992. {{ISBN|0-13-643586-6}}.
* Shanley, Tom. ''IBM PS/2 from the Inside Out''. Addison-Wesley, 1991. {{ISBN|0-201-57056-4}}.

==External links==
{{Commons category|IBM Personal System/2}}
{{external media
| width  = 210px
| float  = right
| video1 = [https://www.youtube.com/watch?v=6Aud7-qMFgM IBM PS/2 commercial (1988)] {{break}}<small>(Courtesy [[Centre for Computing History]]. For copyright reasons: See [[Template:PD-US-1989|PD-US-1989]]. [https://publicrecords.copyright.gov/advanced-search?page_number=1&parent_query=%5B%7B%22operator_type%22:%22AND%22,%22column_name%22:%22keyword%22,%22type_of_query%22:%22phrase%22,%22query%22:%22IBM%22%7D,%7B%22operator_type%22:%22OR%22,%22column_name%22:%22keyword%22,%22type_of_query%22:%22phrase%22,%22query%22:%22PS%2F2%22%7D%5D&records_per_page=100&system_of_origin=%5B%22voyager%22%5D&sort_order=%22asc%22&highlight=true&type_of_work=%5B%22visual_material%22,%22motion_picture%22,%22music%22,%22kit%22,%22dramatic_work_choreography%22,%22sound_recording_text%22,%22sound_recording_music%22,%22map%22,%22unspecified%22%5D&model=%22%22&date_field=%22representative_date%22&start_date=%221987-01-01%2000:00:00%22&end_date=%221990-01-01%2000:00:00%22 No records found].)</small>
}}
*[http://retropc.org/index.html?action=w_podrazdela&id_podrazdel=145&id_soderjanie=91 IBM Type 8530]
*[http://www.lenovo.com/psref/pdf/ps2book.pdf IBM PS/2 Personal Systems Reference Guide] 1992 - 1995
*[http://www.computercraft.com/docs/ps2sect.shtml Computercraft - The PS/2 Resource Center]
*[https://www.ardent-tool.com/ Ardent Tool of Capitalism - covers all PS/2 models and adapters]
*[http://pinouts.ws/ps-2-keyboard-pinout.html PS/2 keyboard pinout]
*{{webarchive|url=https://web.archive.org/web/20150810162125/http://www.computer-engineering.org/|date=August 10, 2015|title=PS/2 Mouse/Keyboard Interfacing}}
*[https://archive.org/details/IBMPerso1987  Computer Chronicles episode on the PS/2]
*[http://hpholm.dk/L40SX.html IBM PS/2 L40 SX (8543)]

{{IBM personal computers}}

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[[Category:IBM PS/2| ]]
[[Category:x86 IBM personal computers|PS/2]]
[[Category:OS/2]]
[[Category:16-bit computers]]
[[Category:32-bit computers]]
[[Category:Computer-related introductions in 1987]]
[[Category:Products and services discontinued in 1995]]
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