IBM RT PC | 1986
IBM RT PC
The IBM RT PC (RISC Technology Personal Computer) was a family of workstation computers introduced by IBM in 1986. These were the first commercial computers from IBM to be based on a Reduced Instruction Set Computing (RISC) architecture. The RT PC used IBM's proprietary ROMP (RISC System/6000) microprocessor, which was commercialized from the technologies pioneered by IBM Research's 801 experimental minicomputer—the first RISC-based machine. The RT PC supported three operating systems: AIX, the Academic Operating System (AOS), and Pick.
Despite its potential, the specifications of the RT PC were considered “less than impressive” compared to contemporary workstations from other vendors. This lack of power made it less appealing in the competitive market of high-performance workstations. However, IBM was still seen as a serious contender because of its reputation for technological advancements and its ability to potentially close the performance gap. The RT PC’s commercial success was limited, and all models were discontinued by May 1991. IBM then introduced the RS/6000 workstations in 1990, which utilized the new POWER1 RISC processor, marking the end of the RT PC era.
There were two main types of the RT PC: the floor-standing desk-side tower (IBM 6150) and the desktop model (IBM 6151). Both models featured a special processor card slot and machine-specific RAM cards. Each system had one processor slot, one co-processor slot, and two RAM slots.
The RT PC had three versions of processor cards:
The Standard Processor Card (032 card) featured a 5.88 MHz clock speed (170 ns cycle time), with 1 MB of standard memory, expandable via 1, 2, or 4 MB memory boards. An optional Floating-Point Accelerator (FPA) could be added, which featured a 10 MHz National Semiconductor NS32081 floating-point coprocessor. This card was used in the early RT PC models such as the 010, 020, 025, and A25, announced in 1986.
The Advanced Processor Card had a 10 MHz clock speed (100 ns cycle time) and either 4 MB memory on the processor card or external 4 MB ECC memory. It included a built-in 20 MHz Motorola 68881 floating-point processor. The Advanced Processor Card was used in models such as the 115, 125, and B25, announced in 1987.
The Enhanced Advanced Processor Card had a clock speed of 12.5 MHz (80 ns cycle time), with 16 MB of on-board memory, and an advanced floating-point accelerator as a standard feature. This processor card was used in models such as the 130, 135, and B35, announced in 1988.
All RT PC models supported up to 16 MB of memory. Early models were limited to 4 MB due to the DRAM IC capacity, but later models could be upgraded to 16 MB. I/O was provided via eight ISA bus slots. Storage options included 40 MB or 70 MB hard drives, which were upgradeable to 300 MB. External SCSI cabinets could be used for additional storage. The standard configuration also included a mouse, with display options of either 720x512 or 1024x768 pixels. A 4 Mbit/s Token Ring network adapter or a 10BASE2 Ethernet adapter was also standard.
For specialized applications like CADAM (a computer-aided design program), an IBM 5080 or 5085 graphics processor could be added, connected to a high-resolution display like the IBM 5081, offering 1024x1024 pixel resolution.
Additionally, there was the 6152 Academic System, which was essentially a PS/2 Model 60 with a RISC adapter card, providing a bridge for educational institutions to use RT PC’s RISC-based software. This system allowed universities to run the Academic Operating System (AOS) via a LAN TCP/IP interface.
The RT PC used a microkernel architecture, known as the Virtual Resource Manager (VRM), which managed essential hardware like the keyboard, mouse, display, disk drives, and network interface. This allowed the RT PC to run multiple operating systems simultaneously, with the user able to switch between them using a hotkey combination (such as Alt-Tab). The system ran both AIX version 2 and Pick OS through this microkernel. Pick OS was unique because it combined both an operating system and a database, and was popular for retail business applications, with around 4,000 units sold.
AIX v2, the primary operating system for the RT PC, included full TCP/IP networking support, as well as support for SNA (Systems Network Architecture). It also provided networking file systems such as NFS (licensed from Sun Microsystems) and IBM's Distributed Services (DS), which were compatible with IBM’s larger mainframes and midrange AS/400 systems.
A few RT PCs were shipped with AOS, an IBM version of the 4.3BSD Unix operating system, which was offered to U.S. universities at discounted prices. AOS included features like NFS and a nearly ANSI C-compliant C compiler. The RT PC was also a significant stepping stone in the development of the X Window System. At Brown University, X version 9 was ported to the RT, leading to an important protocol change that would eventually lead to the creation of X11.
In terms of market reception, the RT PC received mixed reviews. Personal Computer World noted that it was difficult to understand what made the RT PC stand out from other Unix boxes on the market, especially when combined with a regular PC. The RT's limited floating-point performance and lack of widespread software support from developers contributed to its commercial struggles. It found some success in specific areas like CAD/CAM, scientific research, and education, particularly after offering discounts to universities. The RT PC also found use in business environments with its Pick OS and point-of-sale applications.
Ultimately, about 23,000 units of the RT PC were sold, with roughly 4,000 units going to IBM's development and sales organizations. The system competed with other established workstations, including the Apollo Domain Series 3000, DEC MicroVAX II, and Sun Microsystems Sun-3. Despite its limited success, the RT PC played an important role in IBM's continued development in the RISC architecture field.
