电子信息工程专业专业英语三千字翻译

1 Unit3 computer architecture and microprocessors 3 1 Computer Architecture 1 Computer architecture in computer science is a general term referring to the structure of all or part of computer system The term also covers the design of system software such as the operating system the program that controls the computer as well as referring to the combination of hardware and basic software that links the machines on a computer network Computer architecture refers to an entire structure and to the details needed to make it functional Thus computer architecture covers computer systems microprocessors circuits and system programs Typically the term does not refer to application programs such as spreadsheets or word processing which are required to perform a task but not to make the system run 2 1 Design Elements 3 In designing a computer system architects consider five major elements that make up the system s hardware the arithmetic logic unit control unit memory input and output The arithmetic logic unit performs arithmetic and compares numerical values The control unit directs the operation of the computer by taking the user instructions and transforming them into electrical signals that the computer s circuitry can understand The combination of the arithmetic logic unit and the control unit is called the central processing unit CPU The 2 memory stores instructions and data The input input and output sections allow the computer to receive and send data respectively 4 Different hardware architectures are required because of the specialized needs of systems and users One user may need a system to display graphics extremely fast while another system may have to be optimized for searching a database or conserving battery power in a laptop computer 5 In addition to the hardware design the architects must consider what software programs will operate the system Software such as programming languages and operating systems makes the details of the hardware architecture invisible to the user For example computers that use the C programming language or a UNIT operating system may appear the same from the user s viewpoint although they use different hardware architectures 6 2 Processing Architecture 7 When a computer carries out an instruction it proceeds through five steps First the control unit retrieves the instruction from memory for example an instruction to add two numbers Second the control unit decodes the instruction into electronic signals that control the computer Third the control unit fetches the data the two numbers Fourth the arithmetic logic unit performs the specific operation the addition of the two numbers Fifth the control unit saves the result 3 the sum of the two numbers 8 Early computers used only simple instructions because the cost of electronic capable of carrying out complex instructions was high As this cost decreased in the 1960s more complicated instructions became possible Complex instructions single instructions that specify multiple operations can save time because they make it unnecessary for the computer to retrieve additional instructions For example if seven operations are combined in one instruction then six of the steps that fetch instructions are eliminated and the computer spends less time processing that operation Computers that combine several instructions into a single operation are called complex instruction set computers CISC 9 However most programs do not often use complex instructions but consist mostly of simple instructions When these simple instructions are run on CISC architectures they slow down processing because each instruction whether simple or complex takes longer to decode in a CISC design An alternative strategy is to return to designs that use only simple single operation instruction sets and make the most frequently used operations faster in order to increase overall performance Computers that follow this design are called reduced instruction set computers RISC 10 RISC designs are especially fast at the numerical computations 4 required in science graphics and engineering applications CISC designs are commonly used for non numerical computations because they provide special instruction sets for handling character data such as text in a word processing program Specialized CISC architectures called digital signal processors exist to accelerate processing of digitized audio and video signals 11 3 Open and Closed Architectures 12 The CPU of a computer is connected to memory and to the outside world by means of either an open or a closed architecture An open architecture can be expanded after the system has been built usually by adding extra circuitry such as a new microprocessor computer chip connected to the main system The specifications of the circuitry are made public allowing other companies to manufacture these expansion products 13 Closed architectures are usually employed in specialized computers that will not require expansion for example computers that control microwave ovens Some computer manufacturers have used closed architectures so that their customers can purchase expansion circuitry only from them This allows the manufacture to charge more and reduces the options for the consumer 14 4 Network Architecture 15 Computers communicate with other computers via networks 5 The simplest network is a direct connection between two computers However computers can also be connected over large networks allowing users to exchange data communicate via electronic mail and share resources such as printers 16 Computers can be connected in several ways In a ring configuration data are transmitted along the ring and each computer in the ring examines this data to determine if it is the intended recipient If the data are not intended for a particular computer the computer passes the data to the next computer in the ring This process is repeated until the data arrive at their intended destination A ring network allows multiple messages to be carried simultaneously but since each message is checked by each computer data transmission is slowed 17 In a bus configuration computers are connected through a single set of wires called a bus One computer sends data to another by broadcasting the address of the receive and the data over the bus All the computers in the network look at the address simultaneously and the intended recipient accepts the data A bus network unlike a ring network allows data to be sent directly from one computer to another However only one computer at a time can transmit data The others must wait to send their messages 18 In a star configuration computers are linked to a central 6 computer called a hub A computer sends the address of the receiver and the data to the hub which then links the sending and receiving computers directly A star network allows multiple messages to be sent simultaneously but it is more costly because it uses an additional computer the hub to direct the data 19 5 Recent Advances 20 One problem in computer architecture is caused by the difference between the speed of the CPU and the speed at which memory supplies instructions and data Modern CPUs can process instructions in 3 nanoseconds 3 billionths of a second A typical memory access however takes 100 nanoseconds and each instruction may require multiple accesses To compensate for this disparity new computer chips have been designed that contain small memories called caches located near the CPU Because of their proximity to the CPU and their small size caches can supply instructions and data faster than normal memory Cache memory stores the most frequently used instructions and data and can greatly increase efficiency 21 Although a large cache memory can hold more data it also becomes slower To compensate computer architects employ designs with multiple caches The design places the smallest and fastest cache nearest the CPU and locates a second large and slower cache farther away This arrangement allows the CPU to operate on the most 7 frequently accessed instructions and data at top speed and to slow down only slightly when accessing the secondary cache Using separate caches for instructions and data also allows the CPU to retrieve an instruction and data simultaneously 22 Anther strategy to increase speed and efficiency is the use of multiple arithmetic logic units for simultaneous operations called super scalar execution In this design instructions are acquired in groups The control unit examines each group to see if it contains instructions that can be performed together Some designs execute as many as six operations simultaneously It is rare however to have this many instructions run together so on average the CPU does not achieve a six fold increase in performance 23 Multiple computers are sometimes combined into single systems called parallel processors When a machine has more than one thousand arithmetic logic units it is said to be massively parallel Such machines are used primarily for numerically intensive scientific and engineering computation Parallel machines containing as many as sixteen thousand computers have been constructed 3 3 VLIW Microprocessors 24 When Transmeta Corp revealed its new Crusoe of processors last month experts weren t surprised to learn that the chips are based on Very Long Instruction Word VLIW technology VLIW has become 8 the prevailing philosophy of microprocessor design eclipsing older approaches such as RISC and complex instruction set computing CISC 25 All microprocessor designs seek better performance within the limitations of their contemporary technology In the 70s of 20th century for example memory was measured in kilobytes and very expensive CISC was the dominant approach because it conserved memory 26 In the CISC architecture there can be hundreds of program instructions simple commands that tell the system to add numbers store values and display results If all instructions were the same length the simple ones would waste memory Simple instructions require as little as 8 bits of storage space while the most complex consume 120 bits 27 Variable length instructions are more difficult for a chip to process though and the longer CISC instructions are especially complex nonetheless to maintain software compatibility modern chips such as Intel s Pentium III and Advanced Micro Devices Inc s Athlon must still work with all troublesome CISC instructions that were designed in the 1980s even though their original advantage memory conservation isn t as important 28 In the 1980s RAM chips got bigger and bigger in capacity while their prices dropped The emphasis in CPU design shifted to relatively simple fixed length instructions always 32 bits long Although this 9 wastes some memory by making programs bigger the instructions are easier and faster to execute 29 The simplicity of RISC also makes it easier to design superscalar processors chips that can execute more than one instruction at a time This is called instruction level parallelism Almost all modern RISC and CISC processors are superscalar But achieving this capability introduced significant new levels of design complexity 30 VLIW chips can cost less burn less power and achieve significantly higher performance than comparable RISC and CISC chips But there are always trade offs One is code expansion programs grow larger requiring more memory Far more important though is that compilers must get smarter A poor VLIW complier will have a much greater negative impact on performance than would a poor RISC or CISC compiler 31 VLIW isn t a magic bullet but it s the new wave in microprocessor design Within a few years it s certain that at least some of your software will be running on VLIW chips 单元 3 电脑体系和微处理器 3 1 电脑体系 电脑体系 在电脑科技中 是一个依据整个或部分电脑结构 的通用术语 这个术语也包含软件系统的设计 例如这个操作系 统 控制电脑的程序 以及依据这个在电脑网络中连接主机的硬 10 件和基本的软件的结合体 电脑体系依据一个整体结构以及需要 使它能操作的细节 电脑体系包含许多电脑系统 微处理器 电 路路合以及系统程序 通常术语不要提到应用程序 例如电子数 据表或字处理 被要求 执行任务但不使制度逃跑 1 设计元素 在计划一个计算机系统 工程师考虑组成系统硬件的五个 主要元素 算术逻辑单元 控制器 存储器 输入设备 输出设 备 算术逻辑单元运行算术和比较数值 控制器通过取得用户指 令并且变换它们成计算机线路能识别的电信号来引导计算机的操 作 这个算术逻辑单元和控制器的混合体被称作中央处理器 中 央处理器 存储器存储指令和数据 输入和输出设备分别接收和 发送数据 因为各种系统和用户的专项需求不同而要求不同的硬件系 统 一个用户可能需要一个系统极端快速地显示图形 与此同时 在一个笔记本电脑中另一个系统可能不得不被优化为搜索一个数 据库或给电池充电 除了硬件设计 工程师必须考虑什么软件程序将运行这个 系统 软件 例如编程语言和操作系统 构造用户看不到的硬件 体系细节 例如 用 C 语言或者 Unix 操作系统的电脑可以达到相 同的用户目标 尽管用了不同的硬件体系 2 处理体系 当计算机执行一个指令 它连续经历五个步骤 第一步 11 控制器从存储器中取指令 例如 一个两数相加的指令 第二步 控制器把指令译码为能控制电脑的电信号 第三步 控制器取数 据 两个数 第四步 算术逻辑单元运行确切的操作 两个数相 加 第五步 控制器保存结果 两数之和 早期计算机仅仅使用简单指令因为执行复杂的指令的电子 成本的费用很高 在二十世纪六十年代随着费用的降低 更多的 复合指令成为可能 复杂的指令 制定多操作的单指令 能节省 时间 因为计算机不再需要取额外的指令 例如 如果一个指令兼备七 个操作 那么其中的六个取指令的步骤被消除了 以及计算机在 运用操作上花费更少的时间 能够兼备几个指令的单操作的计算 机被叫做复杂指令集计算机 数据流通道 然而 大多数的程序不经常使用复合指令 但是大部分由 简单指令组成 当这些简单指令在数据流通道上运作时 它们慢 下来处理 因为每一个指令 无论简单的还是复杂的 在数据流通 道里译码花费更长的时间 一个交替策略是为了返回只是用简单 的单操作指令集设置 使最频繁使用的操作更快为了提高综合性 能 根据这个设计的计算机被称作精简指令集计算机 精简指令 集计算机 精简指令集计算机设计在科技 图形显示和工程估计方面 对被要求的数的计算