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Historical Notes on CISC and RISC: Difference between revisions
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Meanwhile, other chip designers were going in other directions. One, Motorola, started over with a classic 'big' design, the 68000, which resembled a scaled-down version of the VAX in many ways, with 16 general-purpose registers and a complicated instruction set. This would become the CPU for several successful workstations, as well as the original Apple Macintosh line. Later design extensions would complicate this, though not to the extent that the 80x86 design would be.
Still, it was growing clear that the complex instruction sets were growing counter-productive. Thus, many chip designers decided to go in the opposite direction: minimal instruction sets, no microcoding, load/store architectures with few if any operations working on memory directly, large register sets which could be used to avoid accessing main memory whenever possible, and an emphasis on supporting high-level languages rather than assembly programing. This new idea, which was called RISC (reduced instruction set computer), would be the basis several new CPU designs, including the MIPS, the SPARC, the ARM, the PowerPC, and the Alpha. Of these, all but the Alpha remain in use today for certain specialized areas of use, and the ARM in particular has become the ''de facto'' standard for mobile computing, though for the most part the domination by the Windows-x86 system has forced them out of the market for home and business systems.
1) In principle, only a single operation, 'subtract two memory values and branch if the result is negative' (or several variants on this) is sufficient for to allow a Random Access Machine to perform all Turing-computable calculations). There are even (simulated) machines which are designed on this principle, such as the OISC. In practice, of course, such a system would be both tedious and wasteful, especially for the more commonly used operations such as integer arithmetic.
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