The IBM RT (or PC/RT or 6150 in Europe) was a 32-bit RISC machine. In fact 'RT' meant 'RISC Technology' where RISC itself was initials of Reduced Instruction Set Computers. This machine was IBM's first try into the single-user workstation world and was the ancestor of the RS/6000 range.
The advantages of RISC technology were smaller processor chips, since they needed less on-chip storage for the instruction set, faster signal transfer between devices, and faster instruction execution since the reduced set was designed so that most instructions was executed in a single clock cycle.
The RISC processor of the 6150 was called ROMP for Reshearch Office Products Division. Its study started in IBM Texas labs in 1977 and a prototype form ran in 1978
There were two RT models, the floor-standing 6150 and the desktop 6151. The differences between them lie in the positioning of some I/O ports and in the storage options available.
Despite processor incompatibility with MS-DOS software, the 6150 could run PC software thanks to a PC expansion card holding a Intel 80286 and designed to fit in one of the AT compatible slots of the 6150. the motherboard featured four 32-bit expansion slots to hold the ROMP board, an optional floating-point accelerator board, and two 2 MB RAM boards; two 8-bit and six 16-bit PC slots.
The 6150 operating system was called AIX for Advanced Interactive eXecutive. It succeded to IBM OSes. In fact, it was just an Unix System V with Berkeley 4.2 enhancements and IBM adds for the 6150 environment. Among these adds, the VRM (Virtual Ressource Manager) handled the interface between the Unix kernel and the specific 6150 harware it ran on. A DOS shell was also provided for MS-DOS applications.
Nowadays, one finds RISC processors mainly in numerous small devices like PalmTops or mobile phones. Apple and IBM also use them today, the biggest examples being the PowerPC 7455 (G4) and PowerPC G5 Processor, mostly used in the Power Macintosh and Powerbook series of computers. Many Proprietary Unix systems used them up until only a few years ago (Sun, Silicon Graphics).
The original (170ns) processor card supported an optional floating point coprocessor card based on the National Semiconductor NS32081 FPU.
The next generation (100ns) processor card included a Motorola 68881 floating point coprocessor on the CPU card itself.
The final (80ns) processor card supported a huge double-card floating point coprocessor, again in the coprocessor slot.
If you search the Web for ''IBM SA23-1057'' you can download a PDF of the original RT product architecture. Note that the ROMP processor MMU, though a separate integrated circuit (at least initially), is tightly integrated with the RISC core and would not be called a co-processor today.
Thursday 28th April 2016
Byron Adkins (Austin TX USA)
PowerPC story is far from over (2011.) ...from big box IBM iron (up to Power7) to 8+2 core Cell in Playstation 3, 3 core in Xbox360, single core Nintendo Wii, up to 11th generation of AmigaOne x1000 (2 GHz 64bit dualcore, PCI-E 16x) At IBM (Cloud/Linux) Forum we have just learned that 50 $ of TCP/IP traffic is done by non x86 chips...