RISC和CISC处理器之间的区别套装2

微处理器是单个芯片上的处理单元。它是执行计算机CPU核心功能的集成电路。它是使用金属氧化物半导体(MOS)技术构建的多用途可编程硅芯片，该技术是时钟驱动和基于寄存器的。它接受二进制数据作为输入，并根据存储在存储器中的指令规范对其进行处理后提供输出。这些微处理器能够以每秒十亿条指令的速度一次处理128位。

微处理器的特性：

• 指令系统 –
  微处理器执行的一组完整指令称为指令集。
• 字长–
  在一条指令中处理的位数称为字长或字长。字长越大，CPU的处理能力就越大。
• 系统时钟速度–
  时钟速度决定了一条指令在处理器中执行的速度。微处理器的速度由系统时钟控制。时钟速度通常以每秒百万个周期(MHz)和每秒十亿个周期(GHz)来度量。时钟速度被认为是预测处理器性能的一个非常重要的方面。

微处理器分类：
除了基于字长的分类外，分类还基于体系结构，即微处理器的指令集。这些分类为RISC和CISC。

1. RISC：
   它代表精简指令集计算机。它是一种微处理器体系结构，它使用少量统一长度的指令。这些是简单的指令，通常在一个时钟周期内执行。 RISC芯片的设计相对简单且价格便宜。该设计的缺点是，计算机必须重复执行简单的操作才能执行具有大量处理操作的较大程序。
   例如： SPARC，POWER PC等。
2. CISC：
   它代表复杂指令集计算机。这些处理器为用户提供了数百种大小可变的指令。 CISC体系结构包括一整套专用电路，可以以很高的速度执行这些指令。这些指令通过使用复杂的寻址模式与内存交互。 CISC处理器可减小程序大小，因此执行程序所需的存储周期数更少。这样可以提高整体执行速度。
   示例：英特尔架构，AMD
3. 史诗：
   它代表显式并行指令计算。 RISC和CISC处理器的最佳功能结合在该体系结构中。它实现指令的并行处理，而不是使用固定长度的指令。通过使用一组包含基本指令以及并行指令执行信息的复杂指令，可以支持EPIC处理器的工作。它大大提高了这些处理器的效率。

以下是RISC和CISC之间的一些区别：

CISC	RISC
A large number of instructions are present in the architecture.	Very fewer instructions are present. The number of instructions are generally less than 100.
Some instructions with long execution times. These include instructions that copy an entire block from one part of memory to another and others that copy multiple registers to and from memory.	No instruction with a long execution time due to very simple instruction set. Some early RISC machines did not even have an integer multiply instruction, requiring compilers to implement multiplication as a sequence of additions.
Variable-length encodings of the instructions. Example: IA32 instruction size can range from 1 to 15 bytes.	Fixed-length encodings of the instructions are used. Example: In IA32, generally all instructions are encoded as 4 bytes.
Multiple formats are supported for specifying operands. A memory operand specifier can have many different combinations of displacement, base and index registers.	Simple addressing formats are supported. Only base and displacement addressing is allowed.
CISC supports array.	RISC does not supports array.
Arithmetic and logical operations can be applied to both memory and register operands.	Arithmetic and logical operations only use register operands. Memory referencing is only allowed by load and store instructions, i.e. reading from memory into a register and writing from a register to memory respectively.
Implementation programs are hidden from machine level programs. The ISA provides a clean abstraction between programs and how they get executed.	Implementation programs exposed to machine level programs. Few RISC machines do not allow specific instruction sequences.
Condition codes are used.	No condition codes are used.
The stack is being used for procedure arguments and return addresses.	Registers are being used for procedure arguments and return addresses. Memory references can be avoided by some procedures.

请参阅Set-1：RISC和CISC