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The IBM RT (or IBM 6150 series) was a computer workstation sold by IBM and based around IBM's ROMP processor, a spin-off of the IBM 801 pioneered at IBM Research. The system was introduced in 1986 as the RT PC (RISC Technology Personal Computer) and ran AIX 1.x and 2.x, the Academic Operating System (AOS), or the Pick operating system. It was commonly, but incorrectly, known as the PC RT, and IBM later simplified the name. It didn't enjoy much success, and all models were discontinued by May 1991. However, the system spurred further development, as it was followed by IBM's RS/6000 and the corresponding POWER processor line, which was the basis for the PowerPC.



Three models were produced, the 6150, 6151, and 6152. The basic types of machines were the tower model (6150), and the desktop model (6151). All these models featured a special board slot for the processor card.

There were three versions of the 6150/6151 processor card: the standard 032 processor card had a 5.9 MHz clock rate, 1 MB standard memory (expandable via 1 MB, 2 MB or 4 MB memory boards) and optional floating point accelerator.

The Advanced processor card had a 10 MHz clock and either 4 MB memory on the processor card, or external 4 MB ECC memory cards, and featured a built-in 20 MHz Motorola 68881 floating-point processor. The Enhanced Advanced processor card had a cycle time of 80ns, 16 MB on-board memory, while an enhanced advanced floating point accelerator was standard.

I/O was provided by eight ISA bus slots. A typically configured RT came with 4 MB of memory, maxing out at 16 MB, and with a 20, 30 or 40 MB hard drive, upgradable to 300 MB or more with external SCSI cabinets. Also standard were mouse and either a 720×512 or 1024×768 pixel-addressable display and either a 4 MB/s Token Ring network adapter, or a 10Base2 Ethernet adapter.

The IBM 6152 was a hybrid IBM PS/2 Model 60 with a special MicroChannel board version of the 032 processor, dubbed a "crossbow" board. It ran only the AOS operating system, downloaded from another IBM 6150 or 6151 also running AOS, via a LAN TCP/IP interface.


One of the novel aspects of the RT design was the use of a microkernel. The keyboard, mouse, display, disk drives and network were all controlled by a microkernel, called Virtual Resource Manager (VRM), which allowed multiple operating systems to be booted and run at the same time. One could "hotkey" from one operating system to the next using the Alt-Tab key combination. Each OS in turn would get possession of the keyboard, mouse and display. Both AIX version 2 and the Pick operating system were ported to this microkernel. Pick was unique in being a unified operating system and database, and ran various accounting applications. It was popular with retail merchants, and accounted for about 4,000 units of sales.

The primary operating system for the RT was AIX version 2. Much of the AIX v2 kernel was written in a variant of the PL/I programming language, which proved troublesome during the migration to AIX v3. AIX v2 included full TCP/IP networking support, as well as SNA, and two networking file systems: NFS, licensed from Sun Microsystems, and Distributed Services or DS. DS had the distinction of being built on top of SNA, and thereby being fully compatible with DS on the IBM midrange AS/400 and mainframe systems. For the graphical user interfaces, AIX v2 came with the X10R3 and later the X10R4 and X11 releases of the X Window System from MIT, together with the Xt Athena widget set. Compilers for Fortran and C were available.

Some RT-PCs were also shipped with AOS, an IBM port of 4.3BSD to the ROMP.

The RT forced an important stepping-stone in the development of the X Window System, when a group at Brown University ported X version 9 to the system. Problems with reading unaligned data on the RT forced an incompatible protocol change, leading to version 10 in late 1985.

Sales and market reception

The IBM RT had a varied life even from its initial announcement. Most industry watchers considered the RT as "not enough power, too high a price, and too late". Many thought that the RT was part of IBM's Personal Computer line of computers. This confusion started with its initial name, "IBM RT PC". Initially, it seemed that even IBM thought that it was a high end Personal Computer given the initially stunning lack of support that it received from IBM. This could be explained by the sales commission structure the IBM gave the system: salesmen received commissions similar to those for the sale of a PC: not much. With typically configured models priced at $20,000, it was a hard sell, and so the lack of any reasonable commission resulted in a loss of interest by the IBM sales force.

The performance of the RT, in comparison with other contemporaneous Unix workstations, was not outstanding. In particular, the floating point performance was poor, and was scandalized mid-life with the discovery of a bug in the floating point square root routine.

With the RT system's modest processing power (when first announced), and with announcements later that year by some other workstation vendors, industry analysts questioned IBM's directions. AIX for the RT was IBM's first public foray into UNIX. The lack of software packages and IBM's sometimes lackluster support of AIX, plus the sometimes unusual changes from traditional UNIX operating system defacto standards caused most software suppliers to be slow to embrace the RT and AIX. The RT found its home mostly in the CAD/CAM and CATIA areas, with some inroads into the scientific and educational areas, especially after the announcement of AOS and substantial discounts for the educational community. The RT running the Pick OS also found use as shopping store control systems, given the strong database, accounting system and general business support in the Pick OS. The RT also did well as an interface system between IBM's larger mainframes, due to its SNA and DS support, and some of its point of sale terminals, store control systems and also machine shop control systems.

Approximately 23,000 RTs were sold over the lifetime of the product, with some 4,000 going into IBM internal development and sales organizations. Pick OS sales accounted for about 4,000 units of sales.

External links

This entry incorporates text from the RT/PC FAQ .



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