计算机专业英语教程第5版翻译完整版.docx

1、计算机专业英语教程第5版翻译完整版1.1A Closer Look at the Processor and Primary Storage仔细看看处理器和主存储器We have learned that all computers have similar capabilities and perform essentially the same functions, although some might be faster than others. We have also learned that a computer system has input, output, storage

2、, and processing components; that the processor is the “intelligence” of a computer system; and that a single computer system may have several processors. We have discussed how data are represented inside a computer system in electronic states called bits. We are now ready to expose the inner workin

3、gs of the nucleus of the computer system the processor. 我们已经知道，所有的电脑都具有相似的能力，并且在本质上执行相同的功能，尽管一些可能会比另一些快一点。我们也知道，一个电脑系统具有输入，输出，存储和处理部件；处理器是一个电脑系统智能核心，并且一个电脑系统可以有许多个处理器。我们已经讨论过如何在电脑系统内部，用被称作“位”的电子状态来表现数据，现在我们要弄明白电脑系统的核心，即处理器，的内在的工作方式。The internal operation of a computer is interesting, but there reall

4、y is no mystery to it. The mystery is in the minds of those who listen to hearsay and believe science-fiction writer. The computer is a nonthinking electronic device that has to be plugged into an electrical power source, just like a toaster or a lamp.电脑的内部操作很有意思，但确实没有什么神秘可言。所谓的神秘只是存在于那些听信传闻和相信科幻小说作

5、家的人的意识中。电脑就是一种没有思想的需要接通电源的电子设备而已，与烤面包机和台灯差不多。Literally hundreds of different types of computers are marketed by scores of manufacturers 1. The complexity of each type may vary considerably, but in the end each processor, sometimes called the central processing unit or CPU, has only two fundamental s

6、ections: the control unit and the arithmetic and logic unit. Primary storage also plays an integral part in the internal operation of a processor. These three primary storage, the control unit, and the arithmetic and logic unit work together. Lets look at their functions and the relationships betwee

7、n them.不加夸张地讲，市场上有几百种不同类型的电脑在销售.每种电脑在复杂性上可能有很大区别，但归根结底,每种处理器，有时称为中央处理器即cpu，只有两个基本部分:控制单元和计算逻辑单元.主内存在处理器内部操作中也是一个不可缺少的部分.这三个部件-主内存，控制单元和计算逻辑单元-一起工作.然我们看看它们(各自的)功能和它们之间的联系。 Unlike magnetic secondary storage devices, such as tape and disk, primary storage has no moving parts. With no mechanical movemen

8、t, data can be accessed from primary storage at electronic speeds, or close to the speed of light. Most of todays computers use DRAM (Dynamic Random-Access Memory) technology for primary storage. A state-of-the-art DRAM chip about one eighth the size of a postage stamp can store about 256,000,000 bi

9、ts, or over 25,600,000 characters of data!主存与其他的辅助存储器如：磁带、硬盘不一样的是，主存不含有运转部件。由于没有机械运转的需要，主存种数据访问可以到达电子的速度，或接近于光速。当今电脑的主存大多数使用DRAM动态随机存取存储器技术。目前最新的工艺水平是：一块只有大约1/8张邮票大小的DRAM芯片却可以存储大约256,000,000位，约25,6000,000个字符的数据。Primary storage, or main memory, provides the processor with temporary storage for progra

10、ms and data. All programs and data must be transferred to primary storage from an input device (such as a VDT) or from secondary storage (such as a disk) before programs can be executed or data can be processed. Primary storage space is always at a premium; therefore, after a program has been execut

11、ed, the storage space it occupied is reallocated to another program awaiting execution.主存储器，也就是说内存，用于为处理器暂时存放程序和数据。所有的程序和数据在被操作之前必须从输入设备如VDT或者辅助存储器转存到主存储器中。主存储器存储容量通常是相当有限的，因此，在一个程序执行结束，它所占用的存储空间必须被重新分配给其它正在等待执行操作的程序。Figure 1-1 illustrates how all input/output (I/O) is “read to” or “written from” pr

12、imary storage. In the figure, an inquiry (input) is made on a VDT. The inquiry, in the form of a message, is routed to primary storage over a channel (such as a coaxial cable). The message is interpreted, and the processor initiates action to retrieve the appropriate program and data from secondary

13、storage 3.The program and data are “loaded”, or moves, to primary storage from secondary storage. This is a nondestructive read process. That is, the program and data that are read reside in both primary storage (temporarily) and secondary storage (permanently). The data are manipulated according to

14、 program instructions, and a report is written from primary storage to a printer.图 1-1描述了输入/输出设备与主存储器间的读和写过程。在图中，VDT发出一个输入请求，请求是以消息模式通过通道如同轴电缆发送到主存储器。这个查询被解释，处理器发起操作从辅助存储器中调用合适的程序和数据。程序和数据从辅助存储器传送到主存储器中，这是一个非破坏性的读取过程，也就是说，程序和数据同时存在于主存临时保存和辅助存储器永久保存中。根据程序指令的指示，处理器对数据进行操作，并从主存传送一份报告到打印机。A program inst

15、ruction or a piece of data is stored in a specific primary storage location called an address. Addresses permit program instructions and data to be located, accessed, and processed. The content of each address is constantly changing as different programs are executed and new data are processed.程序指令和

16、数据是存储在主存中一个特殊的位置，称为地址空间。通过地址空间可以实现电脑对程序指令和数据的定位、访问和处理。地址空间的内容是经常变化的，这是由于电脑一直在执行不同的程序和数据。Another name for primary storage is random-access memory, or RAM. A special type of primary storage, called read-only memory (ROM), cannot be altered by the programmer. The contents of ROM are “hard-wired” (desig

17、ned into the logic of the memory chip) by the manufacturer and can be “read only”. When you turn on a microcomputer system, a program in ROM automatically readies the computer system for use. Then the ROM program produces the initial display screen prompt.主存储器也称为随机存取存储器，或RAM。还有一种特殊的主存储器，称为只读存储器ROM，这

18、种存储器不能被程序更改存放的内容。ROM的内容是被生产商通过硬件电路写入的，并且不能被重写。当你启动电脑，ROM中的一个程序会自动就绪等待电脑系统的调用，然后在显示器中显示开机提示。A variation of ROM is programmable read-only memory (PROM). PROM is ROM into which you, the user, can load “read-only” programs and data. Once a program is loaded to PROM, it is seldom, if ever, changed 4. How

19、ever, if you need to be able to revise the contents of PROM, there is EPROM, erasable PROM. Before a write operation, all the storage cells must be erased to the same initial state.可编程只读存储器PROM是另一种ROM，它可以载入只读的程序和数据，一旦载入，将不再改变。然而，假设果你需要去修正PROM的内容，可以使用可擦可编程只读存储器。 EPROM在进行一次写操作之前，所有的存储单元必须被复原为同一初始状态。A

20、more attractive form of read-mostly memory is electrically erasable programmable read-only memory (EEPROM). It can be written into at any time without erasing prior contents; only the byte or bytes addressed are updated.一种更吸引人的可改写只读存储器是电可擦除可编程只读存储器 (EEPROM)。它可以在任何时候写入，而且不会擦除以前的内容；只会更新被寻址的字节。The EEPR

21、OM combines the advantage of nonvolatility with the flexibility of being updatable in place 6, using ordinary bus control, address, and data lines.电可擦可编程存储器把非易失性优点和可更新、需要更新的地方的灵活性结合起来，修改时使用普通的总线控制线、地址线和数据线。Another form of semiconductor memory is flash memory (so named because of the speed). Flash me

22、mory is intermediate between EPROM and EEPROM in both cost and functionality. Like EEPROM, flash memory uses an electrical erasing technology. An entire flash memory can be erased in one or a few seconds, which is much faster than EPROM. In addition, it is possible to erase just blocks of memory rat

23、her than an entire chip. However, flash memory does not provide byte-level erasure 7. Like EPROM, flash memory uses only one transistor per bit, and so achieves the high density of EPROM.另一种半导体记忆体是闪存意味着速度快。闪存在性价比上处于EPROM和EEPROM之间，它使用电擦写技术。整个闪存的内容可以在一到几秒内被清除，这是远快于EPROM的。另外，它还可以对部分记忆块而不是整个存储器进行清除。然而，闪

24、存并不提供字节级的擦除。像EPROM，闪存只使用一个晶体管每比特，因此可以实现高密度的EPROM。Cache MemoryProgram and data are loaded to RAM from secondary storage because the time required to access a program instruction or piece of data from RAM is significantly less than from secondary storage. Thousands of instructions or pieces of data ca

25、n be accessed from RAM in the time it would take to access a single piece of data from disk storage 8. RAM is essentially a high-speed holding area for data and programs. In fact, nothing really happens in a computer system until the program instructions and data are moved to the processor. This tra

26、nsfer of instructions and data to the processor can be time-consuming, even at microsecond speeds. To facilitate an even faster transfer of instructions and data to the processor, most computers are designed with cache memory. Cache memory is employed by computer designers to increase the computer s

27、ystem throughput (the rate at which work is performed).程序和数据从辅助存储器装载到RAM中是因为对RAM中的程序指令和数据的访问时间要明显的少于从辅助存储器访问。数以千条的指令和数据能被访问而只需花费从硬盘访问一次数据的时间。RAM是数据和程序的重要的高速存放区，事实上，电脑系统不会进行任何操作直到程序指令被传入处理器进行执行，这种指令和数据的传输是需要花费时间的，即使传输速度已经是以纳秒来计算了。为了能更快速的传输指令和数据，大多数电脑设计使用高速缓存。电脑设计者使用高速缓存来提高电脑系统的总处理能力工作效率。Like RAM, cac

28、he is a high-speed holding area for program instructions and data. However, cache memory uses SRAM (Static RAM) technology that is about 10 times faster than RAM and about 100 times more expensive. With only a fraction of the capacity of RAM, cache memory holds only those instructions and data that

29、are likely to be needed next by the processor. Two types of cache memory appear widely in computers. The first is referred to as internal cache and is built into the CPU chip. The second, external cache, is located on chips placed close to the CPU chip. A computer can have several different levels o

30、f cache memory. Level 1 cache is virtually always built into the chip. Level 2 cache used to be external cache but is now typically also built into the CPU like level 1 cache.和RAM一样，高速缓存也是程序指令和数据的高速存储区。然而，高速缓存使用静态RAM技术，这种技术比RAM在速度上要高出10倍，价格上高出100倍。cache只保存内存中那一小部分最有可能被处理器执行的指令和数据。两种类型的cache广泛应用于电脑，第

31、一种被植入cpu中的叫做内部高速存储，第二种是外部高速存储，它位于那些靠近cpu的芯片中。一台电脑可以拥有几个不同级别的高速缓存。一级缓存实际上总是植入芯片中，二级缓存过去常常作为外部高速缓存，但是现在也像一级缓存植入cpu内部。 C+和面向对象的程序设计一些面向对象的程序设计概念在语言间渗透。例如微软Quick Pascal是允许使用对象的第一批语言中的一个。C+有什么使得它是一种适合于开发面向对象程序的语言？如同先前所提到的，答案是类class数据类型。给该语言建立对象之能力的是建立在C结构类型之上的C+类class类型。还有，C+把另外几个特性引入面向对象的程序设计，这些特性并不包含在简

32、单地利用对象的其他一些语言中。C+的优点包括强类型、运算符重载和较少地强调预处理。确实你能使用其他一些产品和采用其他一些语言来进行面向对象的程序设计，但是采用C+的众多好处是显著的。这是为面向对象的程序设计而设计的语言，并非现有语言的式样翻新。面向对象的程序设计是一种程序设计技术，使得你能把一些概念看作各种各样的对象。通过使用对象，你能表示要被执行的任务、它们之间的相互作用和必须观察的某些给定的条件。一种数据结构经常形成某个对象的基础；因此，在C或C+中，结构类型能形成某种基本对象。与对象的通信，如前提到的，能通过使用消息来完成。消息的使用类似于在面向过程的程序中对函数的调用。当某对象收到一个消息时，包含在该对象内的一些方法作出响应。方法类似于面向过程程序设计的函数。然而，方法是对象的一部分。C+的类是对C和C+结构类型的扩充，并且形成了面向对象程序设计所需要的抽象数据类型。类能包含紧密相关的一些条目，它们共享一些属性。更正式地说，对象只不过是类的实例。最终，应该出现包含很多对象类型的类库，你能使用这些对象类型的实例去拼合程序代码。在你更详细地考察这些术语之前，一个好的主意是熟悉与C+和面向对象程序设计相关的另外几个概念，如同下面几节所述的。封装封装指的是每个对象