The Complex History of the Intel i960 RISC Processor
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http://www.righto.com/2023/07/the-complex-history-of-intel-i960-risc.html
The Intel i960 was a remarkable 32-bit processor of the 1990s with a confusing set of versions. Although it is now mostly forgotten (outside the many people who used it as an embedded processor), it has a complex history. It had a shot at being Intel's flagship processor until x86 overshadowed it. Later, it was the world's best-selling RISC processor. One variant was a 33-bit processor with a decidedly non-RISC object-oriented instruction set; it became a military standard and was used in the F-22 fighter plane. Another version powered Intel's short-lived Unix servers. In this blog post, I'll take a look at the history of the i960, explain its different variants, and examine silicon dies. This chip has a lot of mythology and confusion (especially on Wikipedia), so I'll try to clear things up.
The ancestry of the i960 starts in 1975, when Intel set out to design a "micro-mainframe", a revolutionary processor that would bring the power of mainframe computers to microprocessors. This project, eventually called the iAPX 432, was a huge leap in features and complexity. Intel had just released the popular 8080 processor in 1974, an 8-bit processor that kicked off the hobbyist computer era with computers such as the Altair and IMSAI. However, 8-bit microprocessors were toys compared to 16-bit minicomputers like the PDP-11, let alone mainframes like the 32-bit IBM System/370. Most companies were gradually taking minicomputer and mainframe features and putting them into microprocessors, but Intel wanted to leapfrog to a mainframe-class 32-bit processor. The processor would make programmers much more productive by bridging the "semantic gap" between high-level languages and simple processors, implementing many features directly into the processor.
The 432 processor included memory management, process management, and interprocess communication. These features were traditionally part of the operating system, but Intel built them in the processor, calling this the "Silicon Operating System". The processor was also one of the first to implement the new IEEE 754 floating-point standard, still in use by most processors. The 432 also had support for fault tolerance and multi-processor systems. One of the most unusual features of the 432 was that instructions weren't byte aligned. Instead, instructions were between 6 and 321 bits long, and you could jump into the middle of a byte. Another unusual feature was that the 432 was a stack-based machine, pushing and popping values on an in-memory stack, rather than using general-purpose registers.
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