What is IBM Multistation?

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IBM Multistation is the nickname for a series of business-oriented personal computers developed and marketed by IBM Japan in the 1980s and 1990s. In the official documents, IBM used the name "Multi-function Workstation" or just IBM 5550.

Historical Context

When the original IBM PC (5150) was released in the United States, it very quickly became a de-facto standard in the personal computer market. At the same time, the transition from 8- to 16-bit computers was taking place in Japan. Some domestic 16-bit personal computers were already released — starting with Mitsubishi Electric Multi-16 and followed by Hitachi MB-16000, Fujitsu FM-11, and NEC PC-9801.

IBM Japan was pressed to release its own personal computer for the local market. The off-the-shelf technology employed by the IBM PC was not capable enough to handle Japanese text. Not without additional hardware.

One of the main issues was the required display resolution. Unless a 16x16 dots per character can be achieved, but Kanji can't be displayed reasonably. The CGA adapter used in the original IBM PC was limited to resolutions up to 640x200 pixels and therefore could display only 12 lines of Kanji per screen. To display the standard 25 lines of text, a video system capable of displaying at least 640x400 pixels per screen would be needed.

To overcome these limitations, IBM Japan developed a custom high-resolution video subsystem. Two different variants were available. A 720x512 pixel system that used 16-dot Kanji characters and a 1024x768 version capable of displaying high-quality 24-dot Kanji characters. As a result of this (and other decisions), the Multistation machines were inherently incompatible with the IBM PC. Something that would later turn out to pose a significant problem.

IBM 5550 Multistation

In 1983, IBM Japan introduced the original IBM 5550 computer — the beginning of what would later become known as the Multistation family.

Following the 5550, a low-end 5540 and a hi-end 5560 models were released. These machines were sold primarily as terminals for users of IBM mainframes or mid-range computers.

By this time, the Japanese market was already crowded with other domestic manufacturers. NEC, in particular, had a very strong position, especially in the home computer segment. The 16-bit NEC PC-9801 replaced not only 8-bit NEC machines but also competing offerings from Fujitsu and Sharp (both of which were strong players in the home computer market previously). IBM Japan tried to compete in the home segment with the PCjr-compatible IBM JX (5511/5510). But the system failed to gain much traction in the marketplace.

While IBM had a slightly better position in the business segment, the reach of the Multistation line remained relatively limited. One of the main problems was its incompatibility with the ubiquitous IBM PC. This meant that none of the widely available and relatively cheap PC hardware and software could be used with the Multistation.

In 1987 IBM (US) released the successor to the IBM PC/XT/AT — the Personal System/2 (PS/2). The PS/2 line introduced many technical advancements, including a new expansion bus called the Micro Channel Architecture (MCA). Despite all these hardware improvements, the new machines maintained software compatibility with the original IBM PC family. IBM Japan decided to base their next-generation personal computers on the PS/2 technology.

In 1987, the first Japanese MCA machine, the 5570, was released. Together with the new architecture came a new name — Personal System/55 (PS/55) — indicating the machine's technological origins and compatibility with the PS/2 line. The PS/55 name was however used even for new additions to the technologically unrelated (non-MCA) Multistation family. The two families also shared the 55xx type range.

The next batch of MCA-based machines included the low-end 5530 and new mid-range models 5550-S/T/V. Many other models followed. IBM also released a few more members of the original Multistation family, but this only lasted for two years (until 1989). By 1991 the Multistation line completely disappeared from the market.

During the first half of the 1990s, IBM Japan continued introducing various new PS/55 products. However, shortly thereafter, the PS/55 and PS/2 lines were discontinued, together with their MCA bus. All subsequent PC-compatible machines produced by IBM were based on "industry-standard" technologies. IBM was never able to restore its domination in the PC market. In May 2005, IBM sold its personal computer business to Lenovo, marking the end of an era.

Name Origins

As for the Multistation or "Multi-function Workstation" name, it reflects the machine's intended use cases and target markets. "One unit, three functions" — Japanese business computer, word processor, and terminal.

Multistation or PS/55?

When the first MCA-based machine was introduced, the name of the series was changed from Multistation to Personal System/55 (PS/55). However, the new machines continued to use model numbers from the 55xx range, leading to confusion among customers and enthusiasts.

The following IBM 55xx machines belong to the original Multistation family:

  • 5550 A, B, C, D, E, G, H, J, K, M, and P
  • 5560 G, H, J, K, M, and P
  • 5540 B, G, J, K, M, and P
  • 5530 G and H
  • 5535 M

All models using the L, N, R, S, T, U, V, W, and Z type suffix are members of the later PS/55 line.

The Y suffix is used by both families.

The Multistation and MCA machines are mutually incompatible.

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