Sidebar: Personal System/2
The Personal System/2 line of IBM computers, or PS/2 for
short, was introduced in April 1987. It was in many ways a radical departure
from the AT - perhaps too radical. The PS/2 had a number of minor and three
major new features: VGA, 1.44MB floppies and Microchannel Architecture
(MCA) bus. Let's take a closer look at these three in order:
In the first PS/2 generation there were four product lines
or models, with each model coming in a number of types with differing amounts
of RAM and storage capacity.
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?)
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.
There were many other PS/2 machines built later, among the
more notable ones were Model 90/95 XP - 486s with XGA graphics, introduced
in 1990. The XGA was one of the first modern accelerator boards, combining
a greatly improved 8514/A accelerator with VGA core. Most accelerator graphics
cards from other companies (S3, ATI and others) were very similar to XGA
in capabilities. IBM also produced PS/2 portables and later laptops.
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
The information presented here was mostly gleaned from 1987
issues of PC Tech Journal which described PS/2 machines in great detail.