The PS/2 used the 72-pin RAM SIMM, which became the de facto standard for RAM modules by the mid-90s in mid-late 486 and early Pentium desktop systems. SIMMs were 32 or 36-bits wide, and replaced the old 30-pin (8/9-bit) SIPP standard, which was much less convenient as SIPPs had to be used four 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
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, relegating the 5.25″ format to an expensive, optional external accessory drive. 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. In the initial line-up, IBM used 720 kB Double Density (DD) capacity drives on the 8086-based models and 1.44 megabytes 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 2.88 MB. The PS/2 floppy drives were famous for not having a capacity detector. 1.44 MB floppies had a hole so that drives could identify them from 720 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 1.44 MB in a PS/2, the resulting floppy only be readable by a PS/2 machine afterwards.
All of the new PS/2 graphics systems (whether MCGA, VGA, 8514, or later XGA) used a 15-pin mini-D connector for video out. This used analog RGB signals, rather than fixed sixteen or sixty-four color lines as on previous CGA and EGA monitors, allowing arbitrary increases in the color depth (or levels of grey) compared to its predecessors. It also allowed for analog grayscale displays to be connected; unlike earlier systems (like MDA and Hercules) this was transparent to software, allowing all programs supporting the new standards to run unmodified whichever type of display was attached. These greyscale displays were relatively inexpensive during the first few years the PS/2 was available, and very commonly purchased with lower-end models. The VGA connector became a near universal standard for connecting monitors and projectors over the course of the early 1990s, replacing a variety of earlier connectors on non-PC hardware. Recently other standards (primarily DVI and HDMI for digital flat panel displays) have become common as well, but none have yet become as common as the VGA connector.
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 EGA standard. VGA increased graphics memory to 256 KiB and provided for resolutions of 640×480 with 16 colors, and 320×200 with 256 colors. VGA also provided a palette of 262,144 colors (as opposed to the EGA palette of 64 colors). The IBM 8514 and later XGA computer display standards were also introduced on the PS/2 line. Although the design of these adapters did not become an industry standard as VGA did, their 1024×768 pixel resolution was subsequently widely adopted as a standard by other manufacturers, and “XGA” became a synonym for this screen resolution. The PS/2 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.
PS/2 systems introduced a new specification for the keyboard and mouse interfaces, which are still in use today and are thus called “PS/2″ interfaces. The PS/2 keyboard interface was electronically identical to the long-established AT interface, but the cable connector was changed from the 5-pin DIN connector to the smaller 6-pin mini-DIN interface. The same connector and a similar synchronous serial interface was used for the PS/2 mouse port. 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.
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 of the MCA bus. Despite all 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 incompatibilities with ISA. IBM offered to sell a Micro Channel license 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.
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) which provided a new protected mode interface and was used by OS/2; the other was named CBIOS (Compatible BIOS) which was included in order for the PS/2 to be software compatible with the PC/AT/XT.
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. However, many of the PS/2s innovations, such as the 1440 kB 3.5-inch floppy disk format, 72-pin SIMM, the PS/2 keyboard and mouse ports, and the VGA video standard, went on to become standards in the broader PC market.
The OS/2 operating system was introduced with the PS/2 line and was intended as its “native” OS, although PC-DOS was also supported. IBM also released AIX PS/2, a Unix-like operating system for PS/2 models with Intel 386 or later processors. Windows was another option for PS/2.
As part of Project Monterey, a beta test version of AIX 5L was released for the IA-64 (Itanium) architecture in 2001, but this was abandoned before it became an official product due to the lack of interest in the finished Project Monterey system, as well as the overall lack of uptake of the IA-64 architecture by a skeptical marketplace, which largely gravitated towards the Project Trillian port of Linux as the primary platform OS.
The Apple Network Server systems were PowerPC-based systems designed by Apple Computer to have numerous high-end features that standard Apple hardware did not have, including swappable hard drives, redundant power supplies, and external monitoring capability. These systems were more or less based on the Power Macintosh hardware available at the time but were designed to use AIX (versions 4.1.4 or 4.1.5) as their native operating system in a specialized version specific to the ANS.
AIX was only compatible with the Network Servers and was not ported to standard Power Macintosh hardware. Not to be confused is A/UX, Apple’s earlier version of Unix for 68k-based Macintoshes.