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Computer Architecture

5 bytes removed, 01:10, 5 September 2014
RISC vs CISC
== RISC vs CISC ==
RISC stands for ''Reduced Instruction Set Computer'' and is a design philosophy favouring a CPU design which executes a small number of simple instructions very quickly. This approach emphasizes the importance of the relies on a good compiler to sequence instructions optimally. Since each instruction is simpler, less silicon is required for instruction decoding and execution, and therefore more silicon is devoted to execution units, cache, and registers to improve performance.
CISC stands for ''Complex Instruction Set Computer'' and is an alternate design philosophy which favours a CPU design where each instruction can perform a lot of work. This approach emphasizes chip logic to optimize performance. Additional sillicon silicon is needed for features such as instruction resequencing, deep pipelines, and more complex execution units.
The RISC vs. CISC debate was at its peak in the 1980s and early 1990s. Most modern CPU designs combine elements of both philosophies. For example, ARM processors, which have historically been considered RISC designs, now include out-of-order execution (a CISC feature); x86 processors (, traditionally regarded as a CISC design) , now feature larger register sets that were originally considered a RISC feature.
== Instruction Set Architecture ==

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