IBM PS/2 | 1987

IBM PS/2

 The PS/2 was IBM's second-generation personal computer. It was released in 1987 and officially replaced IBM's PC, XT, AT, and PC Convertible product lines. PS/2 offered innovative features such as the 16550 UART (serial port), 1440 KB 3.5-inch floppy disk format, 72-pin SIMM, PS/2 ports, and VGA video standard, all of which later became industry standards in the PC market.

The PS/2 line was part of IBM's attempt to regain leadership in the PC market, introducing the exclusive Micro Channel Architecture (MCA) in high-end models. However, models supporting MCA were not compatible with existing IBM PCs, which caused significant controversy in the industry. Most major PC manufacturers opposed IBM's licensing terms for MCA-compatible hardware, particularly the per-device royalty. The OS/2 operating system was released alongside the PS/2 line, and it was initially planned as the primary operating system for models with Intel 80286 or higher processors. However, IBM PC DOS 3.3 was the only available operating system at launch, and OS/2 1.0 (text mode only) and Microsoft Windows 2.0 were released months later. IBM also released the UNIX-based AIX PS/2 operating system for models with Intel 386 or higher processors.

IBM's early PS/2 computers gained popularity in the business market, and by September 1988, 3 million PS/2 units were reported to have been sold in 18 months. However, PS/2 failed in the consumer market. IBM failed to clearly communicate the connection between the OS/2 1.x operating system and PS/2 Micro Channel Architecture to consumers in a way that would justify the PS/2's price premium. In contrast, IBM PC compatible systems maintained industry-standard hardware and could run Microsoft Windows. Competitors also opposed Micro Channel by establishing the EISA bus standard. In 1992, Macworld stated that "IBM had lost its leadership in the market and had become a minor player with its own technology." IBM officially discontinued the PS/2 line in July 1995.

The technical characteristics of the PS/2 were quite different from previous PCs. While the PS/2 was designed to maintain software compatibility with the IBM PC/AT/XT line, its hardware was significantly different. The PS/2 had two BIOS: one was ABIOS, providing a new protected mode interface for OS/2, and the other was CBIOS, included for compatibility with PC/XT/AT software. CBIOS was highly compatible, even including cassette BASIC. While IBM did not release the BIOS source code, it promised to release the BIOS entry points.

The Micro Channel Architecture (MCA) was introduced in some PS/2 models. MCA is conceptually similar to the channel architecture of the IBM System/360 mainframe. MCA was technically superior to ISA and enabled faster communication within the system. The features of MCA later appeared in the PCI standard, with data transfer speeds similar to PCI. MCA supported concurrent transaction management between cards and between cards and the processor, a feature that would later be seen in the PCI-X bus format.

Bus mastering, bus arbitration, and a primitive form of plug-and-play management were some of the advantages of MCA. However, MCA was not widely adopted outside of the PS/2 line.

Whenever a card was installed, users had to use a floppy disk. All interrupts and other changes were made by reading the previous configuration from the floppy disk and writing the new configuration back to the disk. While this was inconvenient for small organizations, it saved time and was cheaper than calling a PC technician for installation. However, in large organizations running hundreds or thousands of PCs, matching each PC to the correct floppy disk became a logistical nightmare. Without the original floppy disk, changes to the PC card could not be made.

Keyboard/Mouse Layout:

The PS/2 IBM Model M keyboard used the 101-key layout of the previous IBM PC/AT extended keyboard. European variants had an additional key next to the left Shift key, resulting in a 102-key configuration.

Interface:

The PS/2 port was once widely used for connecting input devices, and later in the PC 97 specification, the keyboard was designated as purple and the mouse as green. PS/2 systems introduced a new specification for keyboard and mouse interfaces, which is still in use today (though gradually being replaced by USB devices). The PS/2 keyboard interface was inspired by Apple's ADB interface and, electrically, was the same as the older AT interface, but the connector was changed from the 5-pin DIN connector to the smaller 6-pin mini-DIN interface. A similar synchronous serial interface was used for the PS/2 mouse port.

The early desktop models, the Model 50 and Model 60, featured a new cable-less internal design, using an interposer circuit board to connect the internal drives and motherboard. These machines were also easy to disassemble and reassemble without tools, which made maintenance easier.

Additionally, the PS/2 introduced the Extended BIOS Data Area (EBDA), a new software data area. The primary purpose of the EBDA was to add a new buffer area for the dedicated mouse port. To do this, the existing BIOS Data Area (BDA) had to be modified to point to the base address of the EBDA.

Another innovation in the PS/2 was the introduction of bidirectional parallel ports. This allowed parallel ports to function not just for printer connections but also as high-speed data transfer interfaces. This enabled the use of new hardware such as parallel port scanners and CD-ROM drives, and printers were no longer just output devices, but could communicate with the host PC and send back signals.

Graphics:

Most early PS/2 models came with the new video standard, Video Graphics Array (VGA), which replaced the older EGA. VGA increased graphics memory to 256 KB, supported 16 colors at a resolution of 640×480, and supported 256 colors at 320×200. It also provided a palette of 262,144 colors, which was a significant improvement over EGA's 64-color palette. The IBM 8514 and later XGA computer display standards were also introduced with the PS/2 line.

Main monitors and maximum resolutions were as follows:

• 8504: 12", 640×480, 60 Hz non-interlaced, 1991, monochrome
• 8507: 19", 1024×768, 43.5 Hz interlaced, 1988, monochrome
• 8511: 14", 640×480, 60 Hz non-interlaced, 1987
• 8512: 14", 640×480, 60 Hz non-interlaced, 1987
• 8513: 12", 640×480, 60 Hz non-interlaced, 1987
• 8514: 16", 1024×768, 43.5 Hz interlaced, 1987
• 8515: 14", 1024×768, 43.5 Hz interlaced, 1991
• 8516: 14", 1024×768, 43.5 Hz interlaced, 1991
• 8518: 14", 640×480, 75 Hz non-interlaced, 1992
• 9515: 14", 1024×768, 43.5 Hz interlaced, 1992
• 9517: 16", 1280×1024, 53 Hz interlaced, 1991
• 9518: 14", 640×480, non-interlaced, 1992
• 38F4737: 10", 640×480, non-interlaced, 1989, amber monochrome plasma screen, for Models P70 and P75 only

In fact, all XGA 1024×768 monitors were multi-mode monitors, which could transparently pass VGA signals through built-in VGA, so they could support 640×480 resolution at 60 Hz in VGA mode without any restrictions. However, the 95xx models (including some 85xx models) were intended for use with the XGA-2 or Image Adapter/A card and could not synchronize in standard VGA modes due to their higher fixed refresh rates.

The design of graphics adapters, like VGA, did not become an industry standard, but the 1024×768 resolution was widely adopted by other manufacturers, and XGA became synonymous with that resolution. The exception was the 8086-based Models 25 and 30, which used MCGA, a reduced version of VGA.

MCA IBM XGA-2 Graphics Card VGA Video Connector:

All PS/2 graphics systems (MCGA, VGA, 8514, or XGA) used a 15-pin D-sub connector for video output. This connector used analog RGB signals instead of the digital color signals used by earlier CGA and EGA monitors. While digital signals were limited to a fixed 16 or 64-color palette, analog RGB signals allowed for a much wider range of color depth.

Storage:

Some PS/2 models used a quick-connection socket incompatible with the standard 5.25-inch floppy connectors on the back of the floppy drives.

Apple popularized the 3.5-inch floppy disk with the Mac, and IBM introduced it into the PC market with the PC Convertible in 1986. The PS/2 line fully adopted 3.5-inch floppy drives, which became widely adopted in the industry. However, due to the lack of a 5.25-inch drive bay, it was not possible to later integrate CD-ROM drives during the 1990s. The absence of a 5.25-inch floppy drive bay caused issues for PS/2 users, who could not run existing IBM-compatible software directly. However, IBM offered external 5.25-inch floppy drives as an option on early PS/2 models to enable data transfer.

3.5-inch DD and HD Floppies:

In the early lineup, IBM used a 720 KB double-density (DD) drive for 8086-based models and a 1440 KB high-density (HD) drive for models with 80286 and higher processors. By the end of the PS/2 line, 2880 KB became the standard capacity.

PS/2 floppy drives did not have a capacity-detecting function. The 1440 KB floppy had a hole that the drive could detect, preventing the formatting of a 720 KB floppy as 1440 KB. However, since IBM did not implement this feature, it was possible to format a 720 KB floppy as 1440 KB, but such a floppy could only be read by PS/2 systems.

PS/2 used a variety of internal hard drives. Early models used MFM or ESDI drives, while some desktop models used a combination of power/data cables similar to floppy drives. Later models used DBA ESDI or parallel SCSI. Typically, desktop PS/2 models could only have one internal hard drive, though additional storage could be added through optional SCSI interfaces.

Memory:

Later PS/2 models introduced 72-pin SIMMs, which became the de facto standard for RAM modules in 486 and Pentium desktop systems in the mid-1990s. 72-pin SIMMs offered a 32-bit or 36-bit width and replaced the earlier 30-pin SIMM (8/9-bit) standard. The 30-pin SIMM required two or four modules to match the CPU's 16-bit (80286, 80386SX) or 32-bit (80386, 80486) data bus, which was highly inconvenient for Pentium systems. The 72-pin SIMM offered larger capacities (initially 1 MB to 128 MB) and more finely graded capacity options than the 30-pin SIMM.

Many PS/2 models used IBM's proprietary SIMMs, and it was not always possible to use standard SIMMs directly. However, if the existence and type detection bridges or related contacts were rewired correctly, industry-standard SIMMs could be adjusted to fit PS/2 systems.