Taking the RISC Out of CISC

　　已經(jīng)有一個(gè)模糊的定義之間的RISC（精簡(jiǎn)指令集計(jì)算機(jī)）和CISC（復(fù)雜指令集計(jì)算）架構(gòu)的地步，在許多情況下，條款幾乎是毫無(wú)意義的。許多現(xiàn)代的RISC處理器比CISC處理器更復(fù)雜。事實(shí)上，它已不再是RISC和CISC指令定義之間的差異的數(shù)量，而是他們的表現(xiàn)方式的內(nèi)存訪問(wèn)。

　　盡管RISC風(fēng)格建筑的例子可以在1960和1970年代發(fā)現(xiàn)，RISC的真正的歷史可以追溯到上世紀(jì)80年代。它背后的想法是，有一個(gè)更簡(jiǎn)單的指令集，意味著這些指令可以更快地執(zhí)行架構(gòu)如果沒(méi)有指示，很少，如果以往的負(fù)擔(dān)，執(zhí)行。

　　兩種最初的RISC體系結(jié)構(gòu)分別是MIPS和Power體系結(jié)構(gòu)，分別在斯坦福大學(xué)和加州大學(xué)伯克利分校開(kāi)發(fā)。關(guān)鍵的一點(diǎn)是RISC系統(tǒng)使用了負(fù)載存儲(chǔ)結(jié)構(gòu)。這里的內(nèi)存通常是通過(guò)特定的指令訪問(wèn)的，而不是作為其他指令的一部分訪問(wèn)的。今天，當(dāng)RISC系統(tǒng)已經(jīng)變得比CISC架構(gòu)越來(lái)越復(fù)雜，內(nèi)存訪問(wèn)系統(tǒng)看作是一個(gè)決定性的因素在RISC和CISC之間的區(qū)別。在最初的架構(gòu)，早期的例子是休利特帕卡德PA-RISC和Sun公司的SPARC處理器。

　　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.