• VGA or Video Graphics Array was an incremental improvement over IBM's previous standard, EGA. It had 256K memory and offered resolutions up to 640x480 in 16 colors (compared to EGA's 640x350 maximum) plus a brand new low resolution (320x200) mode with 256 simultaneous colors out of a palette of approximately 260,000 colors. This mode made good looking games on the PC possible and was extremely popular well into the 1990s. The MCA equipped PS/2s all had VGA integrated on the motherboard, although IBM was producing ISA VGA cards for use in IBM AT machines too. VGA was widely embraced and clone VGAs started appearing soon. With VGA also came analog monitors allowing unlimited number of colors. VGA is the last adopted graphics hardware standard. All modern graphics cards are compatible with VGA but beyond VGA, there is no standard. PS/2s had one MCA slot designated for a graphics expansion board. In 1987, IBM introduced the 8514/A accelerator card which plugged into this slot. It had no VGA capability (obviously) and allowed up to 1024x768 resolution in 256 colors on cards equipped with 1MB video memory, with the appropriate monitor (IBM 8514, who'd guess that?) of course.
• The introduction of 3.5" high density floppy drives in PS/2 machines was a controversial step. All PS/2s had one 3.5" drive built in and nothing else. While that is perfectly normal today, back in 1987 it was a big problem for many users because no other machines had those drives! This made exchange of software via SneakerNet difficult and somewhat hampered PS/2 acceptance although most users accepted 1.44MB floppies as inevitable progress. Again, 3.5" HD drives are the last widely adopted standard. Larger capacity drives were introduced later (notably 2.88MB drives in later PS/2s and some ThinkPads) but were not widely used.
• MCA was the feature of PS/2 machines and the most controversial by far. It was completely incompatible with the AT (or ISA) bus used in all previous IBM PCs and compatibles. MCA was far more advanced than ISA. It allowed substantially higher transfer speeds (more similar to PCI in the later versions of MCA), busmastering capability, bus arbitration and Plug and Play. Actually it wasn't called Plug and Play back then but MCA adapter cards had no jumpers or switches and were fully software configurable. Higher bus speed had one important implication at that time: computers usually had 1 or 2MB RAM on the motherboard but no provision for expansion. There were RAM expansion boards (usually able to emulate EMS as well) plugged into regular ISA bus. Especially on 386s this was a performance bottleneck on ISA machines. But unlike VGA and 1.44MB floppies, MCA was not widely accepted. There were multiple reasons for this. IBM required licensing fees from manufacturers of MCA systems (not from MCA card makers) in an effort to gain advantage over clone makers. Unfortunately in the end the MCA market was too small. Another problem was that MCA came perhaps too early. On most 286s the ISA was "fast enough" and in 1987 there were no high performance adapters (disk, LAN) that would need MCA for optimum performance. Yet another problem was that PS/2 machines were MCA only which prevented some people from using them - in cases where they needed special adapter cards (data acquisition etc.) only available for the AT bus. In retrospect IBM perhaps should have built one or two ISA slots in PS/2s. MCA did not become a widespread standard and the PC industry had to reinvent most of MCA's features with great pain 5 years later - the new standard is PCI of course.

• Model 30. This was not a 'real' PS/2 as it lacked the MCA and VGA. These machines were equipped with 8MHz 8086 CPUs and MCGA graphics (a hybrid between CGA and VGA). Intended as a replacement for the venerable IBM PC/XT, Model 30s were relatively cheap and sold in large quantities. Later in 1987, IBM introduced very similar Model 25 - a computer and a monitor in a single housing, similar to the Mac.
• Model 50. The first true PS/2 with MCA and VGA. These were desktop machines equipped with 10MHz 80286 CPUs and fast (zero wait state) memory but only slow 20MB fixed disks (or DASD in IBM speak). Intended as a replacement for IBM AT, these machines weren't as popular as IBM hoped. For less money it was possible to buy a faster clone computer from Compaq, AST or ALR.
• Model 60. A bigger brother of Model 50, a tower unit (back then the term 'tower' was not invented yet, it was called 'floor-standing') with 10MHz 80286 and larger and faster drives.
• Model 80. This was the top of the line first generation PS/2. The only machine with 32-bit MCA, it was initially equipped with 16MHz 80386 Intel CPU and up to 115MB ESDI disk. Just like Model 60, Model 80 was a tower unit. Unfortunately for IBM, Compaq beat them to market with Deskpro 386 by several months and what was worse, there was initially a great shortage of Model 80s. But these machines were extremely sturdy and I don't doubt there are still some Model 80s in service.

The PS/2 line was not as successful as IBM hoped. It did not become the new standard even though many features that first appeared in PS/2 machines did become widespread. But IBM sold millions of PS/2s and and there were even MCA based PS/2 clones from Dell, Tandy and NCR among others. Since IBM lost market dominance, no other leader emerged. Thus some standards introduced in the first PS/2s in 1987 (notably 1.44MB floppies and to some extent VGA) were never replaced by anything better.

The history of PS/2 is intertwined with and somewhat parallel to the history of OS/2 (and the name itself is a big hint). IBM tried to sell PS/2s claiming that they would run OS/2 better - the problem was that OS/2 was not available until nearly a year after the PS/2 line was unveiled. This claim was not quite untrue, the MCA was certainly superior to ISA and OS/2 could make better use of it than DOS. But this also made people think that OS/2 would not run on non-PS/2 machines which was not true (in fact IBM itself was supporting OS/2 on its own AT machines). IBM also couldn't market PS/2s - they were unable to explain to people why they should want PS/2 and MCA.

While PS/2 computers did not take over and the line was ultimately discontinued by IBM, the introduction of PS/2 is without any doubt an important milestone in PC history. A great number of innovations that first appeared in the PS/2 line was adopted by the industry (apart from VGA and 1.44MB floppies there were for instance PS/2 keyboards and mice or PS/2 72 pin memory modules). PS/2 machines were built to last and some of them are still happily running, years and years after they were built, a tribute to IBM's conservative, built-to-last engineering so unpopular these days.
 

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