IBM RT PC

IBM RT PC

Company type	Product line
Industry	Computer hardware
Founded	1986 (1986)
Fate	Discontinued in May 1991
Successor	RS/6000 series
Products	Workstation computers
Parent	IBM

The IBM RT PC (short for RISC Technology Personal Computer) represents a series of workstation computers launched by IBM in 1986. These machines marked IBM's initial foray into commercial systems utilizing a reduced instruction set computer (RISC) design, powered by IBM's own ROMP microprocessor. This processor was developed from concepts originally explored in the experimental 801 minicomputer project by IBM Research. The RT PC was compatible with three distinct operating systems: AIX, the Academic Operating System (AOS), and Pick.

Although the RT PC introduced an advanced architectural approach, its technical performance was regarded as somewhat underwhelming relative to other workstations available at the time, with benchmarks suggesting it trailed competitors by roughly eighteen months. Despite this, it was acknowledged as a pivotal step for IBM entering the RISC workstation arena, leveraging the company’s technological expertise. However, these performance drawbacks limited its market impact. IBM succeeded the RT PC with the RS/6000 series in 1990, which incorporated the new proprietary RISC chip, POWER1. Production of all RT PC variants ceased by May 1991.

Hardware

The RT PC was offered in two primary configurations: a tower-style unit designed to stand beside a desk (IBM 6150) and a more compact desktop model (IBM 6151). Both configurations included a dedicated slot for processor cards along with machine-specific RAM modules. Each system contained one processor slot, one co-processor slot, and two slots for RAM expansion.

Three distinct processor card variants were available:

• The Standard Processor Card (also known as the 032 card) operated at 5.88MHz, came equipped with 1MB of memory expandable through additional boards, and supported an optional Floating-Point Accelerator (FPA) board featuring a 10MHz National Semiconductor NS32081 coprocessor. This card powered the initial RT PC models released in January 1986.

• The Advanced Processor Card ran at 10MHz, offering either 4MB of onboard memory or external ECC memory, and integrated a 20MHz Motorola 68881 floating-point unit. An optional Advanced Floating-Point Accelerator (AFPA) board utilizing Analog Devices ADSP-3220/3221 processors was also available. This version was introduced with models launched in February 1987.

• The Enhanced Advanced Processor Card operated at a clock speed of 12.5MHz and included 16MB of onboard memory alongside an improved floating-point accelerator. It was featured in models announced in July 1988.

All RT PCs could accommodate up to 16MB of RAM; however, earlier units were restricted to 4MB due to limitations of DRAM technology at that time. The input/output architecture comprised eight ISA bus slots. Storage options ranged from hard drives sized between 40 and 70MB, with upgrades possible up to 300MB, plus external expansion via SCSI cabinets. Standard peripherals encompassed a mouse and display choices offering resolutions of either 720×512 or 1024×768 pixels. Network connectivity was supported through adapters compatible with Token Ring or 10BASE2 Ethernet protocols.

To boost graphical capabilities—especially beneficial for running IBM’s CADAM computer-aided design software—users could connect an IBM 5080 or IBM 5085 graphics processor alongside the RT PC. The IBM 5080 system supported a high-resolution IBM 5081 display at 1,024-by-1,024 pixels and was housed within a separate cabinet positioned adjacent to the workstation.

6152 Academic System

The 6152 Academic System consisted of an IBM PS/2 Model 60 outfitted with a RISC Adapter Card—a Micro Channel board that housed a ROMP processor, associated support integrated circuits, and up to 8 MB of RAM. This configuration allowed the PS/2 to execute ROMP-based software designed for the AOS, which was transmitted from an RT PC running AOS through a LAN TCP/IP connection.

Software

The RT PC introduced a microkernel named Virtual Resource Manager (VRM), responsible for handling input devices such as keyboard and mouse, display output, disk storage, and network resources. This architecture facilitated the simultaneous operation of multiple operating systems with effortless switching via the Alt-Tab key combination. Both AIX version 2 and the Pick operating system were adapted to run on VRM; Pick integrated both operating system and database functionalities and gained popularity in retail accounting environments, with sales reaching approximately 4,000 units.

AIX version 2 served as the main operating system for the RT, with a significant portion of its kernel implemented in a PL/I dialect, which complicated upgrades to AIX version 3. It featured support for TCP/IP networking protocols, IBM’s Systems Network Architecture (SNA), and two network file systems: Sun Microsystems’ NFS and IBM Distributed Services (DS), which was interoperable with AS/400 and mainframe platforms. The graphical user interface incorporated X Window System versions from X10R3 through X11, utilizing the Athena widget toolkit. Compilers for C and Fortran languages were also provided.

Certain RT PCs were shipped with the Academic Operating System (AOS), IBM’s adaptation of 4.3BSD Unix tailored for academic institutions under special educational pricing. AOS extended BSD by adding NFS capabilities and included an almost ANSI C-compliant compiler. A subsequent iteration based on 4.3BSD-Reno was developed but saw limited adoption.

The RT had an impact on the evolution of the X Window System when Brown University ported version 9 to it; hardware constraints necessitated protocol modifications that ultimately led to the release of X version 10 in late 1985.

Sales and market reception

Debuting in January 1986, the RT PC entered a competitive market featuring established workstations such as Apollo Domain Series 3000, DEC MicroVAX II, and Sun Microsystems’ Sun-3. Industry experts criticized its high price—approximately $40,000 for CAD/CAM setups—and found its graphics and networking capabilities underwhelming. Rival companies welcomed its introduction without perceiving it as a serious competitor.

The RT’s performance was moderate relative to other Unix workstations; its floating-point processing was notably weak and later discovered to contain a square root calculation flaw. Evaluations questioned its cost-effectiveness compared to pairing other Unix workstations with PC clones. Academic users at MIT and Brown University also regarded it as inferior.

Misunderstandings arose because many assumed the RT was part of IBM’s Personal Computer family due to its original designation "IBM RT PC." Sales commissions were aligned with PC products, which hindered sales efforts given typical pricing around $20,000 and resulted in limited enthusiasm from sales personnel.

With limited processing capabilities at launch and constrained software availability—further complicated by IBM’s inconsistent support for AIX and deviations from Unix standards—the RT primarily targeted CAD/CAM applications along with specialized scientific and educational uses following the introduction of AOS and educational discounts. The Pick OS variant achieved success in retail store management systems due to its robust database and accounting features. Additionally, the RT served as an intermediary connecting IBM mainframes with point-of-sale terminals or machine shop control systems via SNA and DS protocols.

During its production run, roughly 23,000 units were sold; around 4,000 units were utilized internally by IBM’s development and sales divisions, while Pick OS deployments accounted for about 4,000 units.

By 1990, IBM controlled only 1.8% of the workstation market. In February 1990, IBM launched the RS/6000 series—which received more favorable reception—and industry observers deemed this release essential following the "disastrous" RT PC experience that had been disparaged by competitors.

As a component of the NSFNET backbone

Starting in 1987, the NSF initiated the deployment of its T1 backbone linking supercomputing centers, utilizing 24 IBM RT-PC units configured as ‘parallel routers’. The favorable performance of this T1 infrastructure paved the way for proposals to upgrade to T3 transmission rates.

The National Science Foundation Network (NSFNET), which served as an early foundation for today’s Internet, operated its T1 backbone network from July 1988 until November 1992. This network employed routers constructed from multiple RT PCs—usually nine—connected through a Token Ring local area network.

Further reading

• — Features four in-depth technical papers on the system’s design and processor technology.

• — IBM document SA23-1057-00

• — Chapter 5 explores the roots of PowerPC architecture in IBM 801 and RT PC systems.

• — Comprehensive narrative on the RT PC’s engineering and market obstacles.

External links

• IBM RT PC information page
• The IBM RT resource page
• Archived JMA Systems FAQ
• Demonstration video of IBM RT PC in use

This article includes material from the RT/PC FAQ.