IBM PS/2
The Personal System/2 or PS/2 was IBM's second generation of personal computers. The PS/2 line, released to the public in 1987, was created by IBM in an attempt to recapture control of the PC market by introducing an advanced proprietary architecture. Although IBM's considerable market presence ensured the PS/2 would sell in relatively large numbers, the PS/2 architecture ultimately failed in its bid to return control of the PC market to IBM. Due to the higher costs of the closed architecture, customers preferred competing PCs that extended the existing PC architecture instead of abandoning it for something new. Two of the PS/2s innovations, the 72 pin SIMM and the PS/2 keyboard and mouse ports became ubiquitous much later.
Technology
IBM's PS/2 was designed to remain software compatible with their PC/AT/XT line of computers upon which the booming PC clone market was built, but the hardware was quite different. PS/2 had two BIOSes. One was named ABIOS (Advanced BIOS) with which OS/2 operating system was running on PS/2. The other was named CBIOS (Compatible BIOS) which was prepared in order for PS/2 to be software compatible with the PC/AT/XT.
Micro Channel Architecture
The IBM Personal System/2 line introduced the Micro Channel Architecture (MCA for short) which was technically superior to the ISA bus and allowed for higher speed communications within the system.
The MCA bus featured many advances that would not be seen in other interface standards until several years later. Transfer speeds were on par with the much later introduced PCI bus 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. Busmastering capability, bus arbitration, and true plug-and-play BIOS management of hardware were all benefits to the MCA bus. The MCA bus was also a 32-bit based architecture, as opposed to ISA which was only 16-bit.
In spite of these technical advantages, the Micro Channel Architecture never gained wide acceptance outside of the PS/2 line due to IBM's anti-clone practices and incompatiblities with ISA. IBM offered to sell a Micro Channel licence to anyone who could afford the royalty, but they not only required a royalty for every MCA-compatible machine sold, but also a payment for every IBM-compatible machine the particular maker had ever made in the past.
Keyboard/mouse interface
PS/2 systems introduced a new specification for the keyboard and mouse interfaces, which are still in use today and are also called "PS/2". The PS/2 keyboard interface was electronically identical to the long-established AT interface, but the cable connector was changed to a 6-pin mini-DIN interface, as was the PS/2 mouse interface.
The keyboard and mouse interfaces are electrically similar with the main difference being that open collector outputs are required on both ends of the keyboard interface to allow bidirectional communication. However normal desktop motherboards will not identify the keyboard and mouse if they are placed on each others sockets.
Laptops generally have a single port which supports either a keyboard or a mouse and also allows one of the devices to be connected to the two normally unused pins in the connector to allow both to be connected at once through a special splitter cable. The mouse interface is somewhat different to RS-232 (which was generally used for mice on PCs without PS/2 ports) but nonetheless many mice were made that could operate on both with a simple wiring adaptor.
In the 386, 486 and Pentium era, the connectors were also seen on some PC clones with non-standard case designs and the PS/2 mouse connector was sometimes seen on a separate backplate on systems using a standard AT case. However PS/2 ports only became the norm much later with the introduction of the ATX form factor. The design decision for identical but incompatible connectors would prove aggravating to consumers. To help alleviate this, PS/2 keyboard and mouse connectors were later color-coded: purple for keyboards and green for mice as defined by the Microsoft PC 97 standard.
USB supports keyboards and mice as generic Human interface device class devices and the vast majority of USB supporting operating systems support such devices with no need for extra drivers. While many current desktop motherboards still ship with PS/2 ports, most laptops and a large number of big brand desktops do not and PS/2 can now be regarded as a legacy interface. Many current keyboards and mice support both USB and PS/2 with a simple wiring adaptor and active adaptors are availible which plug into a USB port and provide a pair of PS/2 ports.
Graphics
Other features were introduced by this new generation of IBM computer systems, such as the change over to the VGA graphics output standard over the previous EGA standard. VGA increased graphics memory to 256 KB and provided for 640x480 resolutions with 16 colors, and in low-res, 320x200 resolution with 256 simultaneous colors from a palette of 262,144. The 8514 and later XGA were other computer display standards introduced by the PS/2 line. Although the design of these adapters did not become an industry standard as VGA was, their standard resolution (1024 by 768 pixels) and the "XGA" name have been influential on many newer graphics systems. The Model 25 and Model 30, however, did not include VGA. On these budget models, IBM opted to use MCGA, which was a stepping stone between CGA and VGA, but unfortunately lacked EGA compatibility.
External storage
Although 3.5" floppy disks were becoming common in the industry by 1987, the PS/2s were the first IBM models to use them as standard. While the disk format itself was standard, IBM chose to use a non-standard form for the disk drives, resulting in very high repair costs as a standard drive could not be retrofitted to a PS/2. (The IBM part was functionally identical to a standard 3.5" floppy drive, but about five times more expensive.) Initially starting out with a 720 KB Double Density (DD) capacity, these soon evolved to 1.44 megabytes High Density (HD), and had by the end of the PS/2 line moved to a somewhat standardized capacity of 2.88 MB.
Memory
The PS/2 introduced 72-pin RAM SIMMs, which became the de facto standard for RAM modules by the mid-90s in mid-late 486 and early Pentium desktop systems. These were 32 or 36 bits wide, and replaced the old 30-pin (8/9 bit) SIMM standard, which was much less convenient as they had to be used 4 at a time to match the bus width of a system with a 32 bit bus. 72-pin SIMMs were also capable of larger maximum capacities.
Models
The PS/2 Models 25 and 30 (IBM 8530) were ISA-based (in other words, essentially IBM PC/AT-like systems in a different form factor). The machines had an ESDI hard drive interface and the drives were available as an optional part, however many of these entry-level machines were sold without hard drives due to the high cost. The Model 25 featured an integrated display to compete with the Apple Macintosh as a low-cost computer for educational environments. Despite shipping with MCGA graphics, these models often shipped with a black and white screen, rather than color.
The higher models were equipped with the Microchannel bus and SCSI hard drives. PS/2 models 50 (IBM 8550-021)and 60 (IBM 8560) used the Intel 80286 processor, the PS/2 models 70 (IBM 8570-81) and 80 used the 80386DX, while the medium-performance PS/2 model 55SX (IBM 8555-081) used the 16/32-bit 80386SX processor.
The PS/2 models 90 (IBM 8590/9590) and 95 (IBM 8595/9595/9595A) used Processor Complex daughterboards holding the CPU, memory controller, Microchannel bus interface, and other system components. The available Processor Complex options ranged from the 20 MHz Intel 80386 to the 90 MHz Pentium and were fully interchangeable. The IBM PC Server 500, which has a motherboard identical to the 9595A, also uses Processor Complexes.
The IBM PS/2E (IBM 9533) was the first Energy Star compliant personal computer. It had a 50 MHz 486SLC processor, an ISA bus, four PCMCIA slots, and an 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.
Marketing
The PS/2's controversial hardware design was tied to a marketing strategy that was similarly unsuccessful. During the 1980s, IBM's advertising of the original PC and its other product lines had frequently used the likeness of Charlie Chaplin. For the PS/2, however, IBM augmented this character with a notorious jingle that seemed more suitable for a low-end consumer product than a business-class computing platform:
"How ya' gonna' do it? PS/2 It! It's as easy as I.B.M."
"How ya' gonna' do it? PS/2 It! The solution is I.B.M."
Another campaign featured the actors from the television show, M*A*S*H playing updated versions of their characters from the series. [1][2]
The profound lack of success of these advertising campaigns led, in part, to IBM's termination of its relationships with its global advertising agencies; these accounts were reported by Wired Magazine (Issue 3.08, August 1995) to have been worth over $500 Million a year, and the largest such account review in the history of business.
Overall, the PS/2 experiment was a commercial disaster from a consumer perspective. With what was widely seen as a technically competent but cynical attempt to gain undisputed control of the market, IBM unleashed an industry and consumer backlash. The firm suffered massive financial losses for the remainder of the decade, forfeited its previously unquestioned position as the industry leader, and eventually lost its status as the largest single manufacturer of personal computers, first to Compaq and then to Dell.
Still, the platform experienced success in the business sector where many people still lived with the motto "Nobody ever got fired for buying IBM". Many models of PS/2 systems saw a production life span that took them well into the late 1990s.