REDUCE INSTRUCTION SET COMPUTERS

Studies of the execution behavious of high level language programes have provided guidance in designing a new type of architecture: the reduced instruction set computer(RISC),Assignment statements predominate,suggesting that the simple movement of data should be optimized.there are also mang if and loop instructions,which suggest that the underlying sequence control mechanism  needs to be optimized to permit efficient piplining.Studies of operand reference patterns syggest that it should be possible to enchance performance by keeping a moderate number of operands in registers.对于高级语言程序执行性能的研究已经为设计新型处理器体系结构，精简指令系统计算机提供了指南。赋值语句占据的优势表明对单纯的数据传送进行优化，还有很多If和loop指令存在，需要优化基本的顺序控制机构，以使流水线作业效率高，操作数引用模式的研究表明，在多个寄存器中保存适当数量的操作数，可能提高性能。There studies have motivated the key characteristics of RISC machines:(1)a limited instruction set with a fixed format,(2)a large number of registers or the use of the compiler that optimized register usage,and emphasis on optimizing the instruction pipleline.这些研究已经形成了RISC机的一些关键特性：（1）有限的固定格式的指令集（2）使用大量的寄存器或使用编译器优化寄存器应用（3）重点优化指令流水线The simple instruction set of the a RISC lends itself to the efficient piplelining because there are fewer and more predictable operations performed per instruction. A RISC insruction set architecture also lends itself to the delayed branch technique,in which branch instruction are rearranged with other instrictions to improve pipleline efficiency.因为每条指令完成少数的且多为可预测的操作，RISC的简单指令系统适合高效流水作业，RISC指令系统体系结构也适合延迟转移技术，在这种技术中，随同其他指令重新安排转移指令以提高流水效率。Although RSIC systems have been defined and designed in a variety of ways by different groups,the key elementd shared by most designs are there:虽然RISC系统已经由不同的企业以各种方式进行了定义和设计，但大多数设计所提出的关键元素还是相同的。A large number of general purpose registers,or the use of complier technology to optimize register usage.用大量的通用寄存器来优化寄存器的使用a limited and simple instruction set有限的简单指令系统An emphasis on optimizing the instruction pipleline.重点优化指令流水线作业1.Instruction execution characteristics指令执行特性To understand the line of the reasoning of the RISC advocates,we begin with a brief review of instruction execution characteristics,The aspects of computation of interest are as follows:为了了解RISC倡导者们的推理思路，首先观察一下指令执行的一些特征，应当关心的计算机特征如下所述。operations performed: These determine the functions to be performed by the processor and its interaction with memory所完成的操作，这些操作决定可处理器要完成的功能以及处理器与存储器的交互operands used: The types of operands and the frequency of their use determine the memory organization for storing them and the addressing modes for accessing them所用操作数，操作数的类型和使用的频率决定了操作数的存储机制和访问这些操作数的编址方式。execution squencing: This determines the control and pipleline organization.执行顺序：决定了控制和流水线机制。2.The use of A large register file大寄存器组的应用The reason that register storage is indicated is that is the fastest available storage device. faster than both main memory and cache,The register file is physically small.generally on the same chip as the ALU and control unit.and emplpys much shorter addresses than addresses for cache and memory,Thus,a strategy is need that will allow the most frequently accessed operands to be kept in registers and to minimize register-memory operations.使用寄存器存储的理由在于它是可用的最快的存储器件，比主存储器和高速缓存都快，寄存器组实际很小，通常与计算机逻辑部件和控制器放在同一芯片上，而且使用比高速缓存和内存储器短很多的地址，因而需要一种允许最频繁访问的操作数保存在寄存器中并使寄存器-存储器操作降至最小的策略。Two basic approaches are possible,on based on software and the other on hardware,The software approach is to rely on the complier to maximize register usage.The complier will attempt to allocate registers to these variables that will be used the most in a given time period.This approach requires the use of sophisticated program-analysis algorithms.The hardware approach is simple to use more registers so that more variables can be held in registers for longer periods of time有两种可以采用的基本用法：一种是基于软件，另一种是基于硬件，软件方法靠编译程序最大限度的使用寄存器，编译程序力图将给定时间周期内最常用的那些变量分配到这些寄存器中，这一方法要求使用复杂的程序分析算法，硬件方法就是简单的使用更多的寄存器，使更多的变量保存在寄存器中供长时间使用。3.Characteristic of reduce instruction set Architecures精简指令系统体系结构特性Although a variey of different approaches to reduced instruction set architecture have been taken,certain characteristics are common to all of them尽管精简指令系统结构的可用方法很多，但对他们而言有一些特性是共同的。The first characteristic is that there is one machine instruction per machine cycle.A machine cycle is defined to be the time it takes to fecth two aperandd from registers,perform an ALU operation.and store the result in a register, Thus,RISC machine  instructions should be no more complicated than,and execute about as fast as,microinstructions on CISC machines,with simple. one-cycle instructions, there is little or no need for microcode.the machine instructions can be hardweired,sunch instructions should execute faster than comparable machine instructions on the other machines,since it is not nessary to access a micro-program control store during instruction execution.第一特性是每个机器周期有一条机器指令，一个机器周期定义为，机器从寄存器组中取出来两个操作数。完成一种算数逻辑部件运算并将结果存入一个寄存器中所使用的时间，RISC机器指令应该不比CISC微指令复杂，并且执行起来也很快，因为简单，所以单周期指令仅需要少量或不需要微代码，机器指令可以是硬连接的。这样指令执行起来比其他机器的类似指令要快，因为在指令执行期间他不必访问为程序控制存储器。A second characteristic is that most operations should be register-to-register, with only simple load and store operations accessing memory.This design feature simplifies the instruction set and therefore the control unit.For example. a RISC instrution set may include only one or two add instructions; the VAX has 25 different add instructions,Another benifit is that sunch an architecture encourages the optimization of register use.so that frequently accessed operands remain in high-speed storage.第二大特性是大多数操作应该是寄存器对寄存器的，仅有简单的取load和存store操作访问存储器，这种设计特点简化了指令系统，因而简化了指令系统，因而简化了控制器,例如，一个RISC指令系统可以包括一两中加法add指令，VAX机则有25中不同的加法指令，另一个好处是这种体系结构促进了对寄存器使用的优化，是的频繁访问的操作数保存在高速存储器中；A third characteristic is the use of simple addressing modes.Almost all instructions use simple register addressing.Servel additional modes,sunch as displacement and PC-relative,may be included.Other more complex modes can be synthesized in software from the simple ones. Agin, this design feature simplifieds the instrution set and the control unit.第三个特性是采用简单的编址方式，几乎所有的指令都采用简单的寄存器编址，集中附加的方式，如可以包括移位，和与pC有关的方式，另外，更为复杂的方式可以简单的方式在软件中合成，需要强调的是，这种简单化了指令系统和控制器。A fianl common characteristic is the use of simaple instruction formats,Gnerally, only one or a few formats are used,Instruction length is fixed and aligned on word boundaries,Feild locations,especailly the op-code decoding and register operand accessing can occur simultaneouly, simplified formats simplify the control unit, Instruction fetching is optimized since world length units are fecthed, this also means that a single instruction does not cross page boundaries.最后一个共同特性是采用简单的指令格式，一般来讲，只是用一种或少数几种格式，指令长度是固定的并按字的边界调整，字段的位置，特别是操作码的位置是固定的，这种设计有很多的优点，使用固定的字段，操作码译码和寄存器操作数访问可同时进行，简化的格式简化了控制器，因为字长单位来读取的，所以取指令也得到了优化，这也表明了一条指令不会跨页。

keyword
reduced insruction set computer(RISC)精简指令系统计算机
pipleline 流水线
compiler编译器；编译程序
branch instruction 转移指令， 分支指令
complex instruction set computer 复杂指令计算机系统
superscalar 超级标量
machine cycle 机器周期
microinstruction 为指令
microcode 微代码,微指令
addressing 寻址 编址
addressing mode 寻址方式
field 字段
algorthm 算法
op-code 操作码
displacement 移位
instruction format 指令格式

关于自己：
没有目标的前行感觉就像是在海面上飘着，对于生活感到很绝望的，对于生活完全没有感觉。不疼不痒的今天，自己想要的太多了，一边舒适着，自己在舒适区待着，完全没有了前进的动了。
有点失控的生活，得有追求，才会有心跳，才能感觉到自己活着的真实，周天看了摔跤吧，爸爸，感觉满满的鸡血。不断坚持着自己，坚持自己那一份对追求的执着，用了20年的时间来练习摔跤。所以说一个人能能做成一件事情，并不是过分依赖于天分，更多一层是后天多一层的努力和坚持。
这本书说实话，开始第一页看计算机简绍的时候，感觉这是一本简单的书籍，但是随着往后看越发的艰难了，陌生的单词数量有点多，感觉自己有点气馁。那有怎样重要的是完成自己与自己的游戏，不然我会感觉到失落的。自己骗自己。不能这样了，用自己现在的设备，去完成自己想完成的事情，不管外界怎么看我，自己还是的坚持下去的。只要没有做伤害别人的事情，没有做伤害社会的事情，为什么不坚持下去呢？感觉自己今天的思路有点乱:
(1)面对别人的恶意，我是选择屈服还是坚持自己
不能懦弱，如果自己屈服了那就是懦弱的事情。