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Unit 1 Hardware I

1.1 A Closer Look at the Processor and Primary Storage

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,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 workings of the nucleus of the computer system-the processor.

我们已经了解到,所有的计算机都有类似的能力,并执行本质上相同的功能,尽管有些可能比其他的快。我们还知道计算机系统有输入、输出、存储和处理组件;处理器是计算机系统的“智能”;一台计算机系统可以有几个处理器。我们已经讨论了数据如何在计算机系统中以电子状态(称为位)表示。现在我们准备揭示计算机系统的核心——处理器的内部工作原理。

  1. capabilities us: [ˌkeɪpəˈbɪlətiz] n. 能力;功能;性能;(军事)力量(capability 的复数)
  2. essentially us: [ɪˈsenʃəli] adv. 本质上,根本上;大体上,基本上
  3. components us: [kəmˈpoʊnənts] n. 部件;组件;成分;分力(component 的复数)
  4. several us: [ˈsevrəl] adj. 不同的,各自的;<法律>单独,各个 pron. 几个,数个
  5. expose us: [ɪkˈspoʊz] v. 暴露,使显露;使面临,使遭受(危险或不快);揭露,揭发;接触,体验;露出,显露(感情);

The internal operation of a computer is interesting, but there really 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 powersource, just like a toaster or a lamp.

计算机的内部系统很有趣,但它真的没有什么神秘之处。那些听信道听途说、相信科幻小说作家的人,心中才会有谜团。计算机是一种不能思考的电子设备,必须插入电源,就像烤面包机或灯一样。

  1. plugged us: [plʌɡd]adj. 堵塞的;塞紧的v. 堵塞;接通电源(plug 的过去分词)
  2. toaster us: [ˈtoʊstər] n. 烤面包炉;用即兴演讲配以雷盖音乐的主持人

Literally hundreds of different types of computers are marketed by scores of manufacturers 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 sections :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 arithmeticand logic unit-work together. Let's look at their functions and the relationships between them.

毫不夸张得讲,数以百计的不同类型的计算机被几十家制造商销售。每种类型的复杂性可能相差很大,但最终每个处理器(有时称为中央处理单元或CPU)只有两个基本部分:控制单元和算术与逻辑单元。主存储器在处理器的内部系统中也起着不可或缺的作用。主存储器、控制单元、算术和逻辑单元这三个一起工作。让我们看看它们的功能和它们之间的关系。

  1. Literally us: [ˈlɪtərəli]adv. 按照字面意义地,逐字地;真正地,确实地;(用于夸张地强调)简直
  2. scores of 许多,大量
  3. manufacturers[经] 制造商;[经] 厂商
  4. fundamental us: [ˌfʌndəˈment(ə)l] adj. 根本的,基本的;必需的,必不可少的;不能再分的 n. 基本原理;基音,基频
  5. arithmetic us: [əˈrɪθmətɪk] n. 算术;演算,计算;数据统计 adj. 算术的
  6. Primary storage[计] 主存储器
  7. integral us: [ˈɪntɪɡrəl]adj. 必需的,必要的;作为组成部分的;完整的;整的,积分的 n. 积分;完整

Unlike magnetic secondary storage devices, such as tape and disk, primary storage has nomoving parts. With no mechanical movement, data can be accessed from primary storage at electronic speeds, or close to the speed of light. Most of today's 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(256 million)bits, or over 25,600,000 characters of data !

与磁带和磁盘等磁性二级存储设备不同,主存储没有活动部件。由于没有机械运动,数据可以以电子速度或接近光速从主存储器中读取。今天的大多数计算机使用动态随机存取存储器(DRAM)技术作为主存储器。最先进的DRAM芯片大约是邮票大小的八分之一,可以存储大约256,000,000位,或超过25,600,000个字符的数据!

  1. magnetic us: [mæɡˈnetɪk] adj. 磁的,磁性的;磁化的;有吸引力的,有魅力的;(航向)根据磁北测定的
  2. tape us: [teɪp] n. 磁带,录音带;录了音的盒式磁带,录了像的盒式磁带;胶带,胶布;(用来绑东西或作界限标记的)布条,线带;(赛跑中的)终点线;卷尺
  3. mechanical us: [məˈkænɪk(ə)l] uk: [məˈkænɪkl]adj. 机械(方面)的;机械般的,呆板的;精通机械的;机械学的,力学的;独家灌录权的n. 技工,机修工;劳工,工匠
  4. Dynamic us: [daɪˈnæmɪk] uk: [daɪˈnæmɪk]adj. 充满活力的,精力充沛的;动态的,发展变化的;力的,动力的 n. 动力,活力;相互作用,动态;动力学
  5. postage us: [ˈpoʊstɪdʒ] uk: [ˈpəʊstɪdʒ]n. 邮资,邮费;一定面额的邮票;邮寄,邮递
  6. state-of-the-art 最先进的技术、应用最新理念的(Advanced technology)

Primary storage, or main memory, provides the processor with temporary storage for programs and data. All programs and data must be transferred to primary storage from an input device (such as a VDT(Video Display Terminals) ) 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 executed, the storage space it occupied is reallocated to another program awaiting execution.

主存储器或内存为处理器提供程序和数据的临时存储器。在执行程序或处理数据之前,必须将所有程序和数据从输入设备(如VDT(视频显示终端))或从辅助存储器(如磁盘)传输到主存储器。主存储空间总是很宝贵的;因此,在程序执行结束之后,它所占用的存储空间被重新分配给等待执行的另一个程序。

  1. temporary us: [ˈtempəreri] adj. 暂时的,临时的;短期的,短暂的 n. 临时雇员,临时工
  2. executed us: [ˈeksɪkjuːtɪd] uk: [ˈeksɪkjuːtɪd] v. 处决;实施;完成(动作);执行(execute 的过去式与过去分词)
  3. premium us: [ˈpriːmiəm] uk: [ˈpriːmiəm] n. 保险费;(正常价格或费用以外的)加付款,加价;很高的价值,额外价值;额外补贴,津贴;奖品,奖金;<美>优质汽油(=premium gas)adj. 高价的,高品质的
  4. occupied us: [ˈɑːkjupaɪd] adj. 忙于……的,从事……的;(床、椅子、房间等)已被占用的;(地方)被占领的,遭侵占的 v. 占用,居住;占(空间或一段时间);(用武力)占领,侵占(occupy 的过去式和过去分词形式)
  5. reallocated us: [ˌriːˈæləkeɪtɪd]再分配 再指派 重新安排

Figure 1-1 illustrates how all input/output(I/O) is "read to" or "written from" primarystorage.

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 coarial cable). The message is interpreted,and the processor initiates action to retrieve the appropriate program and data from secondary storage, The program and data are "loaded", or moved,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 program instructions, and a report is written from primary storage to a printer.

在图中,在VDT上进行了查询(输入)。查询以消息的形式通过信道(如同轴电缆)传送到到主存中。该消息被解释的同时处理器开始执行从二级存储器中检索适当的程序和数据的动作,程序和数据被从二级存储器“加载”或“移动”到主存储器。这是一个非破坏性的读取过程。也就是说,被读取的程序和数据同时驻留在主存储器(临时)和辅助存储器(永久)中。根据程序指令操作数据,并从主存储器向打印机写入报告。

  1. inquiry us: [ˈɪnkwəri; ɪnˈkwaɪəri] uk: [ɪnˈkwaɪəri] n. 询问,疑问;调查,审查; 探查,探询
  2. coarial cable 同轴电缆
  3. interpreted us: [ɪnˈtɜːrprətɪd] uk: [ɪnˈtɜːprətɪd] v. 解释,说明;口译;把……理解为;演绎(interpret 的过去式和过去分词)
  4. initiates us: [ɪˈnɪʃieɪts] uk: [ɪˈnɪʃieɪts] vt. 启动,开始(initiate 的第三人称单数)
  5. retrieve us: [rɪˈtriːv] uk: [rɪˈtriːv]v. 找回,收回;检索(储存于计算机的信息);(狗等)衔回(物品、猎物);挽救,挽回;回忆,追忆;收绕钓鱼线 n. (尤指中枪猎物的)找回;收绕钓鱼线;<古> 恢复的可能性;检索
  6. appropriate us: [əˈproʊpriət] uk: [əˈprəʊpriət] adj. 合适的,相称的 v. 拨出(款项);私占,挪用
  7. nondestructive us: [ˌnɑːndɪˈstrʌktɪv] uk: [ˈnɒndɪsˈtrʌktɪv] adj. 无损的;非破坏性的
  8. reside us: [rɪˈzaɪd] uk: [rɪˈzaɪd] v. <正式>居住,定居;<正式>存在于<正式>(权利、权力等)属于;位(于)
  9. permanently us: [ˈpɜːrmənəntli] uk: [ˈpɜːmənəntli] adv. 永久地;(问题或困难)不断发生地,一直存在地
  10. manipulated us: [məˈnɪpjuleɪtɪd] uk: [məˈnɪpjuleɪtɪd] v. 操作(manipulate 的过去分词)
  11. instructions us: [ɪnˈstrʌkʃ(ə)nz] uk: [ɪnˈstrʌkʃənz] n. 指令;说明(instruction 的复数形式)

A program instruction or a piece of data is stored in a specific primary storage locationcalled an address. Addresses permit program instructions and data to be located,accessed,andprocessed. The content of each address is constantly changing as different programs areexecuted and new data are processed. Another name for primary storage is random-access memory,or RAM. A special type ofprimary storage, called read-only memory (ROM),cannot be altered by the programmer. Thecontents of ROM are "hard wired" (designed into the logic of the memory chip) by themanufacturer and can be "read only". When you turn on a microcomputer system,a programin ROM automatically readies the computer system for use. Then the ROM program producesthe initial display screen prompt.

A variation of ROM is programmable read-only memory (PROM). PROM is ROM intowhich you,the user,can load "read-only" programs and data. Once a program is loaded toPROM,it is seldom,if ever,changed. However,if you need to be able to revise the contentsof PROM, there is EPROM,erasable PROM. Before a write operation,all the storage cellsmust be erased to the same initial state.

A more attractive form of read-mostly memory is electrically erasable programmable read-only memory (EEPROM). It can be written into at any time withouit erasing prior contents;only the byte or bytes addressed are updated.

The EEPROM combines the advantage of nonvolatility with the flexibility of beingupdatable in place, using ordinary bus control, address, and data lines.

Another form of semiconductor memory is flash memory (so named because of thespeed). Flash memory is intermediate between EPROM and EEPROM in both cost andfunctionality.Like EEPROM, flash memory uses an electrical erasing technology. An entireflash memory can be erased in one or a few seconds, which is much faster than EPROM. Inaddition, it is possible to erase just blocks of memory rather than an entire chip.However,flash memory does not provide byte-level erasure. Like EPROM,flash memory uses onlyone transistor per bit, and so achieves the high density of EPROM.

Cache Memory

Program and data are loaded to RAM from secondary storage because the time required toaccess a program instruction or piece of data from RAM is significantly less than fromsecondary storage. Thousands of instructions or pieces of data can be accessed from RAM inthe time it would take to access a single piece of data from disk storage. RAM is essentiallya high-speed holding area for data and programs. In fact,nothing really happens in a computersystem until the program instructions and data are moved to the processor. This transfer ofinstructions 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 aredesigned with cache memory. Cache memory is employed by computer designers to increase thecomputer system throughput (the rate at which work is performed).

Like RAM,cache is a high-speed holding area for program instructions and data.However,cache memory uses SRAM (Static RAM) technology that is about 10 times fasterthan 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 are likely to be needed next by theprocessor. Two types of cache memory appear widely in computers. The first is re ferred to asinternal cache and is built into the CPU chip. The second,external cache, is located on chipsplaced close to the CPU chip. A computer can have several different levels of cache memory.Level 1 cache is virtually always built into the chip. Level 2 cache used to be external cachebut is now typically also built into the CPU like level 1 cache.