The IBM PS/2: 25 Years of PC History

Here’s a fond look back at the Personal System/2 series of PCs, which embarrassed IBM in the late 1980s but shaped the modern PC you know today.

By Benj Edwards, PCWorld    Jul 10, 2012 6:30 am

IBM PS/2 Model 30 adIBM PS/2 Model 30 adTwenty-five years ago, IBM announced the Personal System/2 (PS/2), a new line of IBM PC-compatible machines that capped an era of profound influence on the personal computer market.

By the time of the PS/2’s launch in 1987, IBM PC clones–unauthorized work-alike machines that could utilize IBM PC hardware and software–had eaten away a sizable portion of IBM’s own PC platform. Compare the numbers: In 1983, IBM controlled roughly 76 percent of the PC-compatible market, but in 1986 its share slipped to 26 percent.

IBM devised a plan to regain control of the PC-compatible market by introducing a new series of machines–the PS/2 line–with a proprietary expansion bus, operating system, and BIOS that would require clone makers to pay a hefty license if they wanted to play IBM’s game. Unfortunately for IBM, PC clone manufacturers had already been playing their own game.

In the end, IBM failed to reclaim a market that was quickly slipping out of its grasp. But the PS/2 series left a lasting impression of technical influence on the PC industry that continues to this day.

Attack of the Clones

When IBM created the PC in 1981, it used a large number of easily obtainable, off-the-shelf components to construct the machine. Just about any company could have put them together into a computer system, but IBM added a couple of features that would give the machine a flavor unique to IBM. The first was its BIOS, the basic underlying code that governed use of the machine. The second was its disk operating system, which had been supplied by Microsoft.

When Microsoft signed the deal to supply PC-DOS to IBM, it included a clause that allowed Microsoft to sell that same OS to other computer vendors–which Microsoft did (labeling it “MS-DOS”) almost as soon as the PC launched.

Ad from the April 1987 launch, featuring the former cast of the 'MASH' TV show.

Ad from the April 1987 launch, featuring the former cast of the ‘MASH’ TV show.That wasn’t a serious problem at first, because those non-IBM machines, although they ran MS-DOS, could not legally utilize the full suite of available IBM PC software and hardware add-ons.

As the IBM PC grew in sales and influence, other computer manufacturers started to look into making PC-compatible machines. Before doing so, they had to reverse-engineer IBM’s proprietary BIOS code using a clean-room technique to spare themselves from infringing upon IBM’s copyright and trademarks.

First PC Clone: MPC 1600

In June 1982, Columbia Data Products did just that, and it introduced the first PC clone, the MPC 1600. Dynalogic and Compaq followed with PC work-alikes of their own in 1983, and soon, companies such as Phoenix Technologies developed IBM PC-compatible BIOS products that they freely licensed to any company that came calling. The floodgates had opened, and the PC-compatible market was no longer IBM’s to own.

At least in the early years, that market did not exist without IBM’s influence. IBM’s PC XT (1983) and PC AT (1984) both brought with them considerable innovations in PC design that cloners quickly copied.

Compaq DeskPro 386 adCompaq DeskPro 386 ad. Image: Courtesy of ToplessRobot.comBut that lead would not last forever. A profound shift in market leadership occurred when Compaq released its DeskPro 386, a powerful 1986 PC compatible that beat IBM to market in using Intel’s 80386 CPU. It was an embarrassing blow to IBM, and Big Blue knew that it had to do something drastic to solidify its power.

[Related: The Computer Hardware Hall of Fame]

That something was the PS/2. The line launched in April 1987 with a high-powered ad campaign featuring the former cast of the hit MASH TV show, and a new slogan: “PS/2 It!”

Critics, who had seen more-powerful computers at lower prices, weren’t particularly impressed, and everyone immediately knew that IBM planned to use the PS/2 to pull the rug out from beneath the PC-compatible industry. But the new PS/2 did have some tricks up its sleeve that would keep cloners busy for another couple of years in an attempt to catch up.

Four Initial Models

IBM announced four PS/2 models during its April 1987 launch: the Model 30, 50, 60, and 80. They ranged dramatically in power and price; on the low end, the Model 30 (roughly equivalent to a PC XT) contained an 8MHz 8086 CPU, 640KB of RAM, and a 20MB hard drive, and retailed for $2295 (about $4642 in 2012 dollars when adjusted for inflation).

The most powerful configuration of the Model 80 came equipped with a 20MHz 386 CPU, 2MB of RAM, and a 115MB hard drive for a total cost of $10,995 (about $22,243 today). Neither configuration included an OS–you had to buy PC-DOS 3.3 for an extra $120 ($242 today).

The following chart from IBM offers a more detailed view of the systems available during the 1987 launch, and illustrates just how complex the variety could be.

IBM chart explaining the four PS/2 models announced in April 1987.

IBM chart explaining the four PS/2 models announced in April 1987.

Every unit in the line included at least one feature new to IBM’s PC offerings–and the market in general. In the following sections, I’ll discuss those new features and how they affected the PC industry.

Integrated I/O Functionality, New Memory Standard

From the IBM PC in 1981 through the PC AT in 1984, IBM preferred to keep a minimum of features in the base unit. Instead, it allowed users to extend their systems with expansion cards that plugged into the internal slots. This meant that a 1981 PC, which shipped with five slots, left little room for expansion when it already contained a graphics card, a disk controller, a serial card, and a printer card–a common configuration at the time.

With the PS/2, IBM chose to integrate many of those commonly used I/O boards into the motherboard itself. Each model in the PS/2 line included a built-in serial port, parallel port, mouse port, video adapter, and floppy controller, which freed up internal slots for other uses.

Computers in the PS/2 series also had a few other built-in advancements, such as the 16550 UART, a chip that allowed faster serial communications (useful when using a modem), as well as 72-pin RAM SIMM (single in-line memory module) sockets. Both items became standard across the industry over time.

PS/2 Keyboard and Mouse Ports

An ad describing the IBM Personal System/2.An ad describing the IBM Personal System/2.The built-in mouse port I mentioned earlier is worth noting in more detail. Each machine in the PS/2 line included a redesigned keyboard port and a new mouse port, both of which used 6-pin mini-DIN connectors.

IBM intended the mouse, as a peripheral, to play a major part in the PS/2 system. The company promised a new graphical OS (which I’ll talk about later) that would compete with the Macintosh in windowing functionality.

Even today, many new PCs ship with “PS/2 connectors” for mice and keyboards, although they have been steadily falling out of fashion in favor of USB ports.

New Floppy Drives

Every model in the PS/2 line contained a 3.5-inch microfloppy drive, a Sony-developed technology that, until then, had been featured most prominently in Apple Macintosh computers.

The low-end PS/2 Model 30 shipped with a drive that could read and write 720KB double-density disks. Other models introduced something completely new: a 1440KB high-density floppy drive that would become the PC floppy drive standard for the next 20 years.

IBM’s use of the 3.5-inch floppy drive was new in the PC-compatible world. Up to that point, IBM itself had favored traditional 5.25-inch disk drives. This drastic format shift initially came as a great annoyance to PC users with large libraries of software on 5.25-inch disks.

Although IBM did offer an external 5.25-inch drive option for the PS/2 line, cloners quickly followed suit with their own 3.5-inch drives, and many commercial software applications began shipping with both 5.25-inch and 3.5-inch floppies in the box.


In many ways, the PS/2 line is most notable, historically, for its introduction of the Video Graphics Array standard.

Among its many modes, VGA could display 640-by-480-pixel resolution with 16 colors on screen, and a resolution of 320 by 200 pixels with 256 colors, which was a significant improvement for PC-compatible systems at the time. It was also fully backward-compatible with the earlier Enhanced Graphics Adapter and Color Graphics Adapter standards from IBM.

In addition, the PS/2 line introduced what we now colloquially call a “VGA connector“–a 20-pin D-type socket that also became an industry standard.

The low-end Model 30 shipped with an integrated MCGA graphics adapter that could display a resolution of 320 by 200 pixels with 256 colors as well, but could display only 640 by 480 pixels in monochrome and was not backward-compatible with EGA. MCGA met its end after IBM included it in only a few low-end versions of the PS/2; cloners never favored it.

Micro Channel Architecture

The crowning glory of the PS/2 line’s hardware improvements was supposed to be its new expansion bus, dubbed Micro Channel Architecture. Every initial PS/2 model except the low-end Model 30 shipped with internal MCA slots for use with expansion cards.

The Model 30 included three ISA expansion slots–the type used in the original IBM PC and extended for the PC AT line. Not surprisingly, the rest of the PC-compatible industry utilized the ISA expansion bus as well, so any PC-compatible machine could use almost all the cards created for other PC compatibles.

MCA NIC IBM 83X9648 16-bit expansion cardMCA NIC IBM 83X9648 16-bit-card. Image: Courtesy of Appaloosa, Wikimedia CommonsWith the PS/2, IBM saw the opportunity to create an entirely new and improved expansion bus whose design it would strictly control and license, thus limiting the industry’s ability to clone the PS/2 machines without paying a toll to IBM.

ISA had become slow and limiting by mid-1980s standards. MCA improved on it by increasing the data width from 16 bits to either 16 bits or 32 bits (which allowed more data to transmit over the bus at a time) and by improving the bus speed from 8MHz to 10MHz.

MCA also introduced a limited form of plug-and-play functionality, wherein each expansion card carried with it a unique 16-bit ID number that a PS/2 machine could identify to help it automatically configure the card.

In theory, that method sounded much easier than the jumper-setting necessary on earlier ISA cards; but in practice, it turned a bit unwieldy. Older IBM Reference Disks (the utilities that set the system’s basic CMOS settings) would not know the IDs for newer cards, which required IBM to release frequent Reference Disk updates. So unless you always had the latest version (which was impossible in the pre-Internet-update era), you probably needed a specially designed disk to use your new MCA expansion card.

The PC clone industry did not take kindly to the power play represented by IBM’s new MCA bus. Just one year after its introduction, a consortium of nine PC clone manufacturers introduced its own rival standard, EISA, which extended the earlier ISA bus to 32 bits with minimal licensing cost. Ultimately, few desktop PCs utilized EISA. The standard remained 16-bit ISA slots until Intel’s introduction of PCI, yet another new bus standard, in the early 1990s.


MCA did not help the PS/2’s fortunes, but another major factor worked to sink the PS/2 as a successful platform.

The high-end Model 80 PS/2The high-end Model 80 PS/2As previously mentioned, IBM planned to release the PS/2 with a completely new, proprietary operating system called OS/2, which would take advantage of new features of the 386 CPU in the high-end Model 80, utilize the built-in mouse port, and also provide a graphical windowing environment comparable to that of the Apple Macintosh.

There was only one problem: IBM hired Microsoft, creator of PC-DOS (and MS-DOS and Windows), to make it.

At the time, Microsoft was enjoying a boom in business from all the MS-DOS licenses it was selling to PC clone vendors, and a proprietary PC OS was most definitely not in its best interest.

So, when IBM announced that the full version of OS/2 would be delayed until late 1988 (with a simple DOS-like preview version coming in late 1987), more than a few conspiracy theories flew around the industry.

Meanwhile, Microsoft was prepping a launch of Windows 2.0, which would have most of the features of OS/2, in late 1987–over a year before IBM would launch OS/2. The situation was a painful lesson in letting your competitor create products for you. Amazingly, IBM did not recognize (and act against) that potential conflict of interest.

The End of IBM’s PC Dominance

After launch, the IBM PS/2 line sold well for a short time (about 1.5 million units sold by January 1988), but its comparatively high cost versus PC-compatible brands steered most consumer-level users away from the systems.

Even worse for IBM, just about every advance it made in the PS/2 ended up being matched (or cloned) and then surpassed by the clone vendors. Sales of the PS/2 slipped dramatically through the rest of the 1980s, and the PS/2 line became an embarrassing public disaster for IBM.

By 1990, it was abundantly clear that IBM no longer guided the PC-compatible market. And in 1994, Compaq replaced IBM as the number one PC vendor in the United States.

IBM stuck with the PC market until 2004, when it sold its PC division to Lenovo. By that time IBM had scored a few more consumer PC innovations with graphics standards and portable computers (especially with the ThinkPad line), but none of its machines after the PS/2 would have the same impact as those it released in the early and mid-1980s.


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