Taking the RISC Out of CISC

　　Taking the RISC Out of CISC

　　已经有一个模糊的定义之间的RISC（精简指令集计算机）和CISC（复杂指令集计算）架构的地步，在许多情况下，条款几乎是毫无意义的。许多现代的RISC处理器比CISC处理器更复杂。事实上，它已不再是RISC和CISC指令定义之间的差异的数量，而是他们的表现方式的内存访问。

　　尽管RISC风格建筑的例子可以在1960和1970年代发现，RISC的真正的历史可以追溯到上世纪80年代。它背后的想法是，有一个更简单的指令集，意味着这些指令可以更快地执行架构如果没有指示，很少，如果以往的负担，执行。

　　两种最初的RISC体系结构分别是MIPS和Power体系结构，分别在斯坦福大学和加州大学伯克利分校开发。关键的一点是RISC系统使用了负载存储结构。这里的内存通常是通过特定的指令访问的，而不是作为其他指令的一部分访问的。今天，当RISC系统已经变得比CISC架构越来越复杂，内存访问系统看作是一个决定性的因素在RISC和CISC之间的区别。在最初的架构，早期的例子是休利特帕卡德PA-RISC和Sun公司的SPARC处理器。

　　CISC products， on the other hand， are typified by the x86 architectures， mainly from Intel but also from others such as AMD. Intel’s Pentium range is one of the best examples of CISC chips， Motorola’s 68000 series is another. However， CISC chips， despite the name， do not always use a complex architecture and these days many are less complex than RISC chips. Basically anything that does not use the load-store memory access system is often classed as CISC， whatever the architecture looks like. There is no doubt that a floating-point RISC architecture is much more complex than， say， an 8-bit CISC processor. Even the addressing modes on RISC chips are often more complex than with many CISC processors. Good examples of modern RISC processors are Microchip’s PIC® range and the devices from many manufactures that are based on ARM™ cores.