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RISC(Reduced Instruction Set Computer) A computer architecture that reduces chip complexity by using simpler instructions. The most widely used RISC microprocessors are the ARM chips found in every smartphone and tablet (see ARM chips).
In order to perform the more comprehensive instructions found in the traditional CISC computers (complex instruction set computers), such as Intel's ubiquitous x86 line, RISC compilers have to generate software routines to perform the equivalent processing.
RISC and CISC All Over the Place
RISC designs date back to the 1960s; however, commercial RISC CPUs became popular with chips from companies such as MIPS and Sun in the late 1980s. When first introduced, RISC CPUs were typically faster than their CISC competitors; however, advancements in CISC technology over the years narrowed the performance differences. For example, Intel's CISC-based x86 architecture, which debuted in the early 1980s, grew exponentially due to ever expanding personal Windows usage. Even the RISC-based PowerPC chips used in Apple computers for more than a decade gave way to CISC-based Intel chips in 2006 (see Mactel). However, due to the low power consumption of RISC chips, smartphones and tablets are almost entirely RISC based (see ARM chips).
|No Microcode Conversion|
|RISC processors execute faster because they have no microcode conversion layer, thus eliminating translation overhead. RISC keeps instruction size constant and bans the indirect addressing mode, retaining only those instructions that can be overlapped and made to execute in one machine cycle or less. However, RISC compilers must generate more instructions than CISC compilers. See microcode, indirect addressing and compiler.|