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PRINCIPLES OF COMPUTER ARCHITECTURE phần 3

bộ nhớ. Vì lý do này, nhiều chương trình đăng ký là nhanh hơn so với các chương trình tương đương với bộ nhớ chuyên sâu, ngay cả nếu nó có hoạt động đăng ký nhiều hơn để làm nhiệm vụ tương tự mà sẽ yêu cầu hoạt động ít hơn với các toán hạng nằm trong bộ nhớ. | 112 CHAPTER 4 THE INSTRUCTION SET ARCHITECTURE Register Register Source 1 Source 2 Figure 4-6 An example datapath. memory. For this reason register-intensive programs are faster than the equivalent memory intensive programs even if it takes more register operations to do the same tasks that would require fewer operations with the operands located in memory. Notice that there are several busses inside the datapath of Figure 4-6. Three busses connect the datapath to the system bus. This allows data to be transferred to and from main memory and the register file. Three additional busses connect the register file to the ALU. These busses allow two operands to be fetched from the register file simultaneously which are operated on by the ALU with the results returned to the register file. The ALU implements a variety of binary two-operand and unary one-operand operations. Examples include add and not or and multiply. Operations and operands to be used during the operations are selected by the Control Unit. The two source operands are fetched from the register file onto busses labeled Register Source 1 rs1 and Register Source 2 rs2 . The output from the ALU is placed on the bus labeled Register Destination rd where the results are conveyed back to the register file. In most systems these connections also include a path to the System Bus so that memory and devices can be accessed. This is shown as the three connections labeled From Data Bus To Data Bus and To Address Bus. CHAPTER 4 THE INSTRUCTION SET ARCHITECTURE 113 The Instruction Set The instruction set is the collection of instructions that a processor can execute and in effect it defines the processor. The instruction sets for each processor type are completely different one from the other. They differ in the sizes of instructions the kind of operations they allow the type of operands they operate on and the types of results they provide.This incompatibility in instruction sets is in stark contrast to the .