An instruction is made up of operations which specify the function to be performed and operands that represent the data to be manipulated. For example， if an instruction is to perform the operation of adding two numbers， it must know what the two numbers are and where the two numbers are. When the numbers are stored in the computer’s memory， they have an address to indicate where they are， so if an operand refers to data in the computer’s memory， it’s called an address. The processor’s job is to retrieve instructions and data from memory and to perform each operation. Having done that， it signals memory to send the next instruction.
The step by step operation is repeated over and over again at speeds measured in millions of a second. A timer called a clock releases precisely timed electrical signals that provide a regular heartbeat for the processor’s work. Megahertz， which means million cycles per second， are used to measure the computer’s speed. A processor is composed of two functional units — a control unit and an arithmetic/logical unit — as well as a set of special workspaces called registers.
1．TheArithmetic and Logic Unit
The arithmetic and logical unit performs the calculations on the numbers and words in the computer. The main operations are addition， subtraction， multiplication and division. Most computers can also perform certain logical operations on words.
The arithmetic and logical unit （ALU） is the functional unit that provides the computer with logical and computational capabilities. Data are brought into the ALU by the control unit， and the ALU performs whatever arithmetic or logic operations are required to help carry out the instruction.
2．The Control Unit
The control unit is the functional unit that is responsible for supervising the operation of the entire computer system. It makes the connections between various functional units of the computer system and calls into operation each unit that is required by the program currently in operation.
The first phase of control is to provide signals to activate the operations in the ALU， the memory unit and the input/ output units. After completing an instruction， the control calls for the next instruction from the memory unit. Usually， the instructions are stored in an increasing order of address. An instruction counter is used in the control unit to record the address of the instruction under examination. By incrementing the address counter， the control unit turns to the next instruction to be fetched.
The control unit fetches instructions from memory and determines their types or decodes them. It then breaks each instruction into a serious of simple small steps
or actions. By doing this， it controls the step by step operation of the entire computer system.
3．Registers
A register is a storage location inside the processor. Register in the control unit are used to keep track of the overall status of the program that is running. Control unit registers store information such as the current instruction， the location of the next instruction to be executed， and the operands of the instruction. In the ALU， registers store data items that are added， subtracted， multiplied， divided， and compared. Other registers store the results of arithmetic and logical operations.
An important factor that affects the speed and performance of a processor is the size of the registers. Technically， the term word size describes the size of an operand register， but it is also used more loosely to describe the size of the pathways to and from the processor. Currently， word sizes in general purpose computer range from 8 to 64 bits.
【Vocabulary】
processor
n. 处理器
instruction
n. 指令
instruction set
指令系统
peripheral
adj. 外围的 n. 外围设备
arithmetic
n. 算术、算法
operation
n. 操作、操作码指令
decode
vt. 解码、解译
operand
n. 操作数
register
n. 寄存器
megahertz
n. 兆赫兹
bit
n. 位、比特
control unit
控制单元
machine language
机器语言
trigger pulse
触发脉冲
【参考译文】
计算机处理器
处理器是解释和执行指令的功能单元，它是计算机的中枢神经系统，与处理器和内存周围被称为外设的设备如键盘、显示器、磁盘等形成对比。每一套处理器都有一套独特的操作命令，例如加、存储、调入等之类的操作命令称为处理器的指令集。计算机系统设计者喜欢将计算机称为机器，所以该指令系统有时也称为机器指令系统，而书写机器指令的二进制语言叫做机器语言。但是不要将处理器的指令系统与BASIC或PASCAL这样的高级程序设计语言相混淆。
一条指令由代表执行特定功能的操作和代表被操作数据的操作数组成。例如，如果一条指令执行两个数相加的操作，那么必须知道这两个数是什么以及这两个数在什么位置。当这两个数存储到了计算机的内存中，它们就有了一个地址指示它的位置。一个操作数只是数据在计算机内存中的位置称为地址。处理器的任务就是从内存中检索指令和数据，执行每一条指令，在完成指令后指示内存送出下一条指令。
一次又一次地执行这些操作步骤，以百万次每秒计算它的速度。一个被称为时钟的计时器准确地发送定时信号，为处理器的工作提供规则的频率。一兆赫兹表示每秒一百万次循环，用它来衡量计算机的速度。每个处理器有两个功能单元，控制单元和算术逻辑单元，和一组称作寄存器的特殊工作空间组成。
1．算术逻辑单元
算术逻辑单元在计算机内执行数字和字符的运算，主要的操作有加法、减法、乘法和除法，大多数计算机也能够执行特定的字符逻辑运算。
算术逻辑单元（ALU）是为计算机提供逻辑及计算能力的部件。控制部件将数据输入算术逻辑部件，然后由算术逻辑部件完成执行指令所需的任何算术或逻辑运算。
2．控制单元
控制单元是负责监控整个计算机系统操作的功能部件。它将计算机系统的各个功能部件连接起来，并按照当前运行程序的需要对每个部件进行操作。
控制单元的第一个步骤是提供信号来激活存储在ALU、内存单元和输入输出单元中的操作指令，完成一个指令后，控制单元从内存中调出下一个指令。通常情况下，指令按照地址的上升序列存储。控制单元中使用指令计数器记录正在校验的指令地址，通过递增地址计数器控制单元指向所要取出的下一条指令。
控制单元从存储器中取出指令，并确定其类型或对其进行译码。然后将每条指令都分解成一系列简单的小步骤。这样它就控制了整个计算机系统的步进操作。
3．寄存器
寄存器是处理器内的存储单元。控制部件中的寄存器用来跟踪正在运行的程序的总体状态。控制器寄存器存储当前指令、下一条将要执行的指令地址以及该指令的操作数等信息。在算术逻辑部件中，寄存器存放要进行加、减、乘、除及比较的数据项。而其他寄存器则存放算术和逻辑运算的结果。
影响处理器速度和性能的一个重要因素是寄存器的大小。从技术上讲，术语“字长”描述了操作数寄存器的大小，但它也可用于简单描述出处理器的通道的大小。现在通用的计算机的字长从8位到64位不等。
【Reading Material】
VLIW Microprocessors
When Transmute Crop revealed its new Crusoe family 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 the prevailing philosophy of microprocessor design， eclipsing older approaches such as RISC and complex instruction set computing （CISC）.
