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计算机专业英语教程第5版翻译

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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 th e 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.

我们已经知道,所有的计算机都具有相似的能力,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,一个计算机系统具有输入,输出,存储和处理部件;处理器是一个计算机系统智能核心,并且一个计算机系统可以有许多个处理器。我们已经讨论过如何在计算机系统内部,用被称作“位”的电子状态来表现数据,现在我们要弄明白计算机系统的核心,即处理器,的内在的工作方式。

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

计算机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家的人的意识中。计算机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 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 arithmetic and logic unit —work together. Let’s look at their functions and the relationships between them.

不加夸张地讲,市场上有几百种不同类型的计算机在销售.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 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 bits, 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达到电子的速度,或接近于光速。当今计算机的主存大多数使用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 programs 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 executed, 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” primary 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 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 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 instruction 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计算机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,这是由于计算机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” (designed into the logic of the memory chip) by the manufactur er 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。当你启动计算机,ROM中的一个程序会自动就绪等待计算机系统的调用,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-on ly” programs and data. Once a program is loaded to PROM, it is seldom, if ever, changed [4]. However, 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,若果你需要去修正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还原为同一初始状态。

A 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 EEPROM 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 memory 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 rather 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 Memory

Program 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 can 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 transfer 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 system 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,计算机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,大多数计算机设计使用高速缓存。计算机设计者使用高速缓存来提高计算机系统的总处理能力(工作效率)。

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 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 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 of 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广泛应用于计算机,第一种被植入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。一台计算机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。

2.1

Optical laser disk technology eventually may make magnetic-disk and magnetic tape storage obsolete. With this technology, the read/write head used in magnetic storage is replaced by two lasers. One laser beam writes to the recording surface by scoring microscopic pits in the disk, and another laser reads the data from the light-sensitive recording surface. A light beam is easily deflected to the desired place on the optical disk, so an access arm is not needed.

光盘技术最终可能使磁盘和磁带存储淘汰。用这种技术,磁存储器所用的读/写头被两束激光代替。一束激光通过在光盘上刻制微小的凹点,对记录表面进行写;而另一束激光用来从光敏感的记录表面读取数据。由于光束容易被偏转到光盘上所需要的位置,所以不需要存取臂。

Optical laser disks are becoming a very inviting option for users. They are less sensitive to environmental fluctuations, and they provide more direct-access storage at a cost that is much less per megabyte of storage than the magnetic-disk alternative. Optical laser disk technology is still emerging and has yet to stabilize; however, at present there are three main categories of optical laser disks. They are CD-ROM, recordable CD-R and rewritable CD-RW, and magneto-optical disk.

对用户而言,光盘正成为最有吸引力的选择。它们(光盘)对环境变化不太敏感,并且它们以每兆字节比磁盘低得多的存储器价格提供更多的直接存取存储器。光盘技术仍在出现,并且还需要稳定;然而,目前有三种主要类型的光盘。它们是CD-ROM、WORM盘和磁光盘。

CD-ROM

Introduced in 1980, the extraordinarily successful CD, or compact disk, is an optical laser disk designed to enhance the recorded reproduction of music. To make a CD recording, the analog sounds of music are translated into their digital equivalents and stored on a 4.72-inch optical laser disk. Seventy-four minutes of music can be recorded on each disk in digital format by 2 billion digital bits. With its tremendous storage capacity, computer-industry entrepreneurs immediately recognized the potential of optical laser disk technology. In effect, anything that can be digitized can be stored on optical laser disk: data, text, voice, still pictures, music, graphics, and video.

1980年引入的,非常成功的CD,或紧密盘是设计来提高音乐的录音重放质量的光盘。为了制作一张CD,把音乐的模拟声音转换成等价的数字声音,并且存储在一张4.72英寸的光盘上。在每张光盘上可以用数字格式(用20亿数字位)记录74分钟的音乐。因为它的巨大存储容量,计算机工业的企业家们立刻认识到光盘技术的潜力。事实上,任何可以被数字化的东西都能存储在光盘上:数据、正文、声音、静止图象、音乐、图形和视频。

CD-ROM(pronounced cee-dee-ROM) is a spinoff of audio CD technology. CD-ROM stand for compact disk-read only memory. The name implies its application. CD-ROM disks, like long-playing record albums, are “pressed” at the factory and distributed with their prerecorded contents(for example, the complete works of Shakespeare or the first 30 minutes of Gone with the wind). Once inserted into the disk drive, the text, video images, and so on can be read into primary storage for processing or display; however, the data on the disk are fixed—they cannot be altered. This is in contrast, of course, to the read/write capability of magnetic disks.

CD-ROM(读作C—D—ROM)是音频CD技术的副产品。CD-ROM代表紧密盘—只读存储器。该名字隐含了它的应用。只读光盘与 (能长期播放的) 唱片一样,在工厂里“压制”并带着预先录好的内容 (如莎士比亚全集,或电影“飘”的前30分钟部分),分发出去。一旦光盘插入光盘驱动器,正文、视频图像等等就能读入主存进行处理或显示;然而,在只读光盘上的数据是固定的—它们不能被改变。当然,这是与磁盘的读/写能力不同的。

The tremendous amount of low-cost dir-access storage made possible by optical laser disks has opened the door to many new applications.

大量的、低成本直接存取存储器(是光盘使之成为可能)已经打开了通向许多新应用的大门。

CD-R AND CD-RW

CD-R and CD-RW both allow user to store data on compact discs, but only data on rewriteable CDs can be erased and overwritten. CD-R discs can only be written to once. Both types of discs look very similar to CD-ROM discs. Recordable CDs are commonly used to store music files, allowing home users to make high-quality personalized music CDs. CD-RW discs can be written to and erased similar to floppy disk. Consequently, they are a good alternative for large file storage, as well as for creating a “master” disc before burning a CD-R discs(most CD-RW drives can write to both CD-RW and CD- R discs, but some CD and CD-R drives cannot read CD-RW discs). CD-R and CD-RW drives also read CD-ROM discs. However, CDs will be eclipsed BY DVDs, once that technology becomes improved and standardized.

CD-R和CD-RW都允许用户存储数据在光盘上,但是只有那些在可复写cd中的数据能被擦除和重写。Cd-r光盘只能被写入一次。这俩种光盘看起来与只读cd光盘差不多。可记录cd管片通常用于存储音乐文件,这样可以允许家庭用户制作高质量的个人音乐唱片。Cd-rw光盘就像软盘那样能被重写和擦除。因此,他们是大容量文件存储的另一种不错选择,同时也作为主盘在对cd-r光盘进行刻入之前(大多数的可擦写光盘驱动器可以读取cd-rw和cd-r光盘,但是也

有一些cd驱动器和cd-r驱动器不能读cd-rw光盘)。Cd-r和cd-rw驱动器也可以读cd-rom光盘,然而,cd将会被dvd 所替代,一旦dvd的技术完全成熟和标准化。

Magneto-Optical Disk

Magneto-Optical disk offers promise that Optical laser disks will become commercially viable as a read-and-write storage technology. The 5and1/4inch disks can store up to 1,000Mb. At present, magneto-optical disks are too expensive and do not offer anywhere near the kind of reliability that users have come to expect of magnetic media. In addition, the access times are relatively slow, about the same as a low-end Winchester disk.

磁光盘有希望使得激光盘成为商业上可行的读/写存储技术。5*1/4英寸的磁光盘可以存储高达1000Mb。目前磁光盘太贵且根本未达到用户对磁介质所期望的那种可靠性。此外,存取时间相对而言比较慢,大约与低档温彻斯特盘相同。

As optical laser disk technology matures to reliable, cost-effective, read/write operation, it eventually may dominate secondary storage in the future as magnetic disks and type do today.

随着光盘技术成熟到可靠,性能价格合算,可读/可写,将来它最终会象现在磁盘、磁带那样统治二级存储器。

DVDs

The acronym DVD(for digital versatile disc, or digital video disc) refer to a relatively new high-capacity optical storage format that can hold from 4.7GB to 17GB, depending on the number of recording layers and discs sides being used. A standard single layered, single-sided DVD can store 4.7GB of data; a two-layered standard enhances the single-side layer to 8.5GB. DVD can be double-sided with a maximum storage of 17GB per disc. The DVD was initially developed to store the full contents of a standard two-hour movie, but is now also used to store computer data and software. DVD-ROM technology is seen by many as the successor to music CDs, computer CD-ROMs, and prerecorded VHS videotape that people buy and rent for home viewing-in other words, read-only products. DVD-R is DVD rewritable(similar to CD-W). The user can write to the disk only once. DVD-RW is DVD recordable(similar to CD-RW). The user can erase and rewrite to the disk multiple times. Only one-sided disks can be used for both DVD-R and dvd-rw. Most DVD drives can play both computer and audio CDs, but you can’t play DVDs in a CD drive.

这个缩写影碟(数字化视频光盘或数字视频光盘),指的是相对较新的高容量光存储格式取决于光盘记录层和边数,可以从4.7 GB的持有以17 GB,被使用。一个标准的单层单面的DVD可以存储4.7 GB的数据,一两个层次的标准,增强了单面层到8.5 GB的。 DVD可双面的每件17 GB的最大存储。该DVD最初是存储标准的全部内容的两个小时的电影,但现在还用于存储计算机数据和软件。DVD - ROM技术是被许多人视为对音乐CD,电脑光盘和人们购买和租赁的预先录制的家庭录影带的后续,换句话说,只读的产品。DVD-R是可记录的DVD(就像CD-R那样)。用户可以对其进行一次写入。DVD-RW是可擦写的(类似的CD - RW),用户可擦除和重写磁盘多次。DVD-R和DVD-RW都是单面光盘。所有的DVD驱动器可以同时播放电脑和音频CD。但是,不能在CD播放机上应用DVD光盘。

DVD Forum Receives Top Information Technology Industry Award for Creation of Unified Specification for Next Multimedia Era

DVD论坛因建立下一代数字多媒体的统一规范而获得最高信息技术工业奖

The DVD Forum today announced that it has received the 1997 PC Magazine Award for Technical Excellence in the category of “Standards”, in recognition of the Forum’s successful development of the dvd-rom specification.

DVD论坛今天宣布,因该论坛成功制定了DVD-ROM规范而获得1997年PC杂志的 (制定标准的) 卓越技术奖。

“New standards are particularly important, since they promise to bring higher levels of technology innovation and market compatibility to today’s technology users,” said by Michael J. Miller, editor-in-chief of PC Magazine.” DVD-ROM is a compelling technology that was chosen because it’s a familiar format that brings a wealth of new computing, educational, gaming and entertainment possibilities to the user.”

“新的标准特别重要,因为它们承诺把更高级的技术革新和市场兼容性带给今天的技术用户,”PC杂志主编Michael J.

Miller说,“DVD-ROM是被选出的激发兴趣的技术,因为它是一种熟悉的格式,它把大量的新计算、新教育、新游戏和新娱乐的可能性带给用户。”

In the Award citation to DVD-ROM technology, PC Magazine referred to DVD as the format that will ”replace the CD-ROM as the primary means of PC content distribution. ”R epresentatives of three companies involved in development of the specification, Hitachi Ltd. , Matsushita Electric Industrial Company(Panasonic) and Toshiba Corporation, accepted the award on behalf of the DVD Forum in a ceremony held on November 17 at COM DEX’ 97 in Las Vegas.

在对DVD-ROM技术的颁奖词中, PC杂志称,DVD将会“代替CD-ROM作为PC内容 (即各种软件和资料) 传播的主要手段。”参加规范开发的三个公司的代表(日立,松下,东芝)以DVD论坛的名义在11月7日,Las Vegas COMDEX '97 举行的庆祝典礼上接受该项奖。

“Products based on specifications defined by the DVD Forum are now shipping in volume to the worldwide computer an d consumer electronics markets, and the Award for Technical Excellence adds to the market’s validation of the success of the standards process, ”said Koji Hase, General Manager of the DVD Products Division at Toshiba Corporation and a founding member of th e DVD Forum. ”We are extremely pleased to see the work of the DVD Forum recognized as one of the key technical achievements in the personal computer industry, particularly as the Forum expands the scope of its work with a large, global membership in 1998. ”

“基于DVD论坛定义的规范的产品现在正在大量运往世界各地的计算机和电子产品市场,并且卓越技术奖增加了市场对成功制定标准的认可,”东芝公司DVD产品部总经理和DVD论坛创办成员Koji Hase说,“我们非常高兴地看到DVD 论坛的工作被公认为个人计算机工业中重要的技术成就之一,特别是在1998年与更大的,全球的会员扩大了它的工作范围。”

“The members of the DVD Forum developed the DVD-ROM specification as the best technical approach and also the best approach for customers in the marketplace, ”said Sakon Nagasaki, director of the DVD Business Development Office of Matsushita Electric Industrial Co. Ltd(Panasonic). “Acceptance of the format illustrates how standards – m aking efforts advance the goals of the entire electronics industry. ”“DVD论坛的成员把DVD-ROM规范开发作为最好的技术方法和对市场上客户的最好方法”松下有限公司的DVD商业开发办公室主任Sakon Nagasaki说,“该格式的接受说明了制定标准如何加快整个电子工业的目标的实现。”

In addition to its role in development of DVD-ROM and DVD-Video standards, the Forum has proposed the format for recordable DVD, known as DVD-R, and rewritable DVD, known as DVD-RAM, to international standards bodies. Work is also continuing on definition of a DVD Audio specification.

除了论坛在开发DVD-ROM和DVD-Video标准的作用外,论坛也提出了可记录DVD的格式,称为DVD-R和可重写的DVD,称为DVD-RAM,并提交国际标准组织。定义DVD-Audio规范的工作也正在继续着。

“The mi sson of the DVD Forum is to define a smooth migration from CD to DVD technology by working with the widest possible representative group of manufacturers and technology end-users in the converging industries of computers and cusumer electronics, ”said Dr. Yoshita Tsunoda, a member of the Exective Staff of Hitachi, Ltd. And Chairman of the DVD Forum’s DVD-RAM Working Group. “The different working groups have already completed definition of three separate DVD technology standards, and we have begun work on de veloping next generation specifications that will provide compatible products well into the next century.”

“DVD论坛的任务是,在汇合计算机工业和消费电子产品工业中,通过与最广泛代表性的制造商与技术最终用户小组一起工作,确定从CD技术向DVD技术的平滑过渡的途径。”日立有限公司执行官之一和DVD论坛DVD-RAM工作组主席Yoshita Tsunoda博士说,“不同工作组已完成三个不同的DVD技术标准的定义,并且我们已开始开发下一代规范的工作,这些规范将很好地提供可兼容产品到下一世纪。”

Recipients of the PC Magazine Awards for Technical Excellence are named by a team of editors, senior contributors and PC Labs personnel after months of evaluation and discussion. PC Magazine, the sponsor of the Technical Excellence Awards, is a 1.175 million circulation magazine published by Ziff-Davis Inc. Pc Magazine is published 22 times a year in print, quarterly on CD, and continuously on the World Wide Web ().

PC杂志的卓越技术奖的获得者是由编辑、捐助者和PC实验室全体成员组成的小组在几个月的评价和讨论后提名。PC 杂志,卓越技术奖的主办者,是由Ziff-Davis公司出版、有1.175百万冊发行量的杂志。PC杂志一年印刷出版22次,每季度出CD,并且连续地在环球网上。

3.3

Java is designed to meet the challenges of application development in the context of heterogeneous, network-wide distributed environments. Paramount among these challenges is secure delivery of applications that consume the minimum of system resources, can run on any hardware and software platform, and can be extended dynamically.

Java是为了解决在复杂的、大规模分布式网络环境下开发应用程序的挑战而设计的。其中最大的一个挑战是确保交付的程序:占用最少的系统资源,并且能在任何硬件、软件平台下运行,能被动态扩展。

Java originated as part of a research project to develop advanced software for a wide variety of network devices and embedded systems. The goal was to develop a small, reliable, portable, distributed, real-time operating platform. When the project started, C++ was the language of choice. But over time the difficulties encountered with C++ grew to the point where the problems could best be addressed by creating an entirely new language platform. Design an architecture decisions drew from a variety of language such as Eiffel, SmallTalk, Objective, C, and Cedar/Mesa. The result is a language platform that has proven ideal for developing secure, distributed, network based end-user applications in environments ranging from network-embedded devices to the World-Wide-Web an the desktop.

Java最初只是一个为各种网络和嵌入式设备而研究的软件系统的一部分,这个系统的目标是一个小的、可信赖的、可移植的,分布式的、实时的平台。最开始C++语言是这个平台的首选。但随着时间的推移,C++出现了很多问题,有必要开发一个全新的语言平台。我们根据Eiffel, SmallTalk, Objective, C, and Cedar/Mesa等语言来做出决策,结果是开发出了一个理想的、能在从嵌入式网络设备到万维网到桌面等各种环境下方便的开发安全的、分布的、基于网络的应用程序的平台。

`The design requirements of Java are driven by the nature of the computing environments in which software must be deployed.

Java的设计要求是由软件所部署的计算环境的本质决定的.

The massive growth of the Internet and the World-Wide Web leads us to a completely new way of looking at development and distribution of software. To live in the world of electronic commerce and distribution, Java technology must enable the development of secure, high performance, and highly robust applications on multiple platforms in heterogeneous, distributed networks.

互联网和万维网的快速发展带领我们用新的眼光去看待开发和发布软件。在电子商务的时代,Java必须具有开发安全性、高效性、健壮的、大众的、能在多平台和多样化、分布式网络运行的程序。

Operating on multiple platforms in heterogeneous networks invalidates the traditional schemes of binary distribution , release, upgrade, patch, and so on. To survive in this jungle, java must be architecture neutral, portable, and dynamically adaptable.

为了能在异构网络的多个平台上执行二进制发布、升级、修补等计划的环境中发展,Java必须是总体结构不带偏向性的、可移植的、且能动态地自适应的。

The java system that emerged to meet there needs in simple, so it can be easily programmed by most developers; familiar, so that current developers can easily learn java; object oriented ,to take advantage of modern software development methodologies and to fit into distributed client-server application; multithreaded, for high performance in applications that need to perform multiple concurrent activities , such as multimedia; and interpreted ,for maximum portability and dynamic capabilities.

Java系统的出现使得这些需求变得简单,所以可以很容易的被大多数开发人员所使用;大众的,所以现在的开发人员可以很容易的学习Java;面对对象的,利用现代软件开发方法的优势以适应分布式客户端-服务器应用程序;多线程的,用于高性能的执行多个并发活动,如多媒体;解释型的,为了最大的可移植性和动态能力。

Together, the above requirements comprise quite a collection of buzzwords, so let’s examine some of them and their respective benefits before going on.

总的来说,上述包括相当多的专业术语,所以在继续之前先让我们来认识一下它们以及它们所带来的的各种好处。

What's completely new is the manner in which java and its run-time system have combined them to produce a flexible and powerful programming system.

Java和它在运行时的系统能包含有良好的操作性以及强大的编译设计系统是一种全新的方式。

Developing your applications using Java results in software that is portable across multiple machine architectures, operating systems, and graphical user interfaces, secure, and high performance. With Java, your job as a software developer is much easier--you focus your full attention on the end goal of shipping innovative products on time, based on the solid foundation of Java. The better way to develop software is here, now, brought to you by the Java language platform.

使用Java开发您的应用软件所带来的是可在多种机器总体结构、操作系统和图形用户借口间的移植,安全性和高性能。使用Java,你作为软件开发人员的工作室非常容易的--基于Java的基础您可以专注发展和及时创新。开发软件的最好方法在这里,现在,给您带来Java语言平台。

Very dynamic languages like lisp, TCL, and SmallTalk are often used for prototyping. one of the reasons for their success at this is that they are very robust---you don't have to worry about freeing or corrupting memory.

非常具有生命力的语言如lisp、tcl和SmallTalk常常用于充当原型构造技术。他们在这取得成功的其中一个原因是:他们非常强大,您不需要内存的释放或者损坏。

Similarly ,programmers can be relatively fearless about dealing with memory when programming in java .the garbage collection system makes the programmer's job vastly easier ;with the burden of memory management taken off the programmer's shoulders , storage allocation errors go away.

同样的,程序员在使用Java编程的时候可以不用过多担心存储问题。无用单元手机系统使程序员的工作大为容易,卸下了程序员肩上存储管理的负担,存储分配错误不再发生。

Another reason commonly given that like lisp , TCl, and smalltalk are good for prototyping is that they don't require you to pin down decision early on these languages are semantically rich.

一般认为像LISP、TCL和SmallTack这样一些语言十分适合于原型法的另一理由,是因为它们不要求你受早期决定的约束---这样的语言的语义是很丰富的。

Java has exactly the opposite property ; it forces you to make explicit choices . along with these choices come a lot of assistance you can write method invocations and ,if you get something wrong, you get told about it at compile time . you don't have to worry about method invocations error.

Java具有完全相反的性质,它强制你做出明确的选择。伴随着这些选择的是许多助理---如:你可以写一些方法的调用,如果有错误,你会在编译时被告知。您也不需要担心方法调用错误。

4.1

An operating system is the software which acts as an interface between a user of a computer and the computer hardware.操作系统是计算机用户和硬件的软件接口。The purpose of an operating system is to provide an environment in which a user may execute program. 操作系统的目的是提供用户一个可以执行程序的环境。The primary goal of an operating system is thus to make the computer system convenient to use. 操作系统的主要目标因此是使计算机系统便于使用。A secondary goal is to use the computer hardware in an efficient way. 其次是高效地使用计算机硬件。

We can view an operating system as a resource allocator. 我们可以把操作系统看做是一个资源分配器。A computer system has many resources which may be required to solve a problem: CPU time, memory space, file storage, input/output(I/O) devices, and so on.一个计算机系统拥有许多资源,因此需要去解决一些问题,如cpu时间,内

存空间,文件存储,输入输出设备等。The operating system acts as the manager of these resources and allocates them to specific programs and users as necessary for their tasks. 操作系统就像是资源管理员,把资源分配给特定的程序和用户当它们工作需要时。Since there may be many, possibly conflicting, requests for resources, the o/s must decide which requests are allocated resources to operate the computer system fairly and efficiently. 因此有可能会有很多有可能产生冲突的资源请求,操作系统必须决定分配资源给哪个请求能使计算机系统合理和有效的运行。

Early computers were(physically) very large machines run from a console.早期的计算机是从控制台运行的体积非常大的机器。The programmer would write a program and then operate the program directly from the operator’s console. 程序员要写一条程序然后直接从操作者的控制台操作程序。Software such as assemblers, loaders, and compilers improved on the convenience of programming the system, but also required substantial set-up time. 象汇编程序、装入程序及编译程序这样的软件使系统软件编程更方便,但同时也需要大量的启动时间。To reduce the setup time, operators were hired and similar jobs were batched together.[1]为了能减少这些准备时间,操作者就被雇佣,相似的作业成批排在一起。

Batch systems allowed automatic job sequencing by a resident monitor and improved the overall utilization of the computer greatly. 批处理系统通过一个常驻内存的监控程序允许自动的作业定序。The computer no longer had to wait for human operation. 这样计算机就不必再等待用户操作。CPU utilization was still low, however, because of the slow speed of the I/O devices relative to the CPU. Offline operation of slow devices was tried. 然而,CPU使用率仍然不高,这是因为I/O设备的处理速度较CPU慢导致的。

Buffering was another approach to improving system performance by overlapping the input, output, and computation of a single job. 缓冲机制是另一种提高系统系能的方法,它将一条作业的输入、输出和计算工作重叠交错进行。Finally, spooling allowed the CPU to overlap the input of one job with the computation and output of other jobs.最后,伪脱机技术允许CPU将一条作业的输入和其他作业的计算输出交错进行。

Spooling also provides a pool of jobs which have been read and are waiting to be run. 伪脱机也为那些已经被读入并且还在等待运行的作业提供一个作业池。This job pool supports the concept of multiprogramming. 这个作业池支持一种叫做多程序设计的概念。With multiprogramming, several jobs are kept in memory at one time; the CPU is switched back and forth between them in order to increase CPU utilization and to decrease the total real time needed to execute a job. 在这种多程序设计技术中,多个作业可以同时存放在内存中;CPU在这些作业中来回切换控制,以至于增加CPU使用率和减少执行一条作业的总时间。

Multiprogramming, which was developed to improve performance, also allows time sharing. 多道程序设计被开发来提高性能,也允许分时。

Time-shared operating systems allow many users (from one to several hundred) to use a computer system interactive at the same time. 分时操作系统允许多个用户(从一个到几百个)同时交互式地使用计算机系统。As the system switches rapidly from one user to the next, each user is given the impression that he has his own computer. 由于系统迅速地从一个用户切换到下一个用户,每一个用户被给予一种他拥有自己的计算机的印象。Other operating systems types include real-time systems and multiprocessor systems. 其他操作系统类型包括实时系统和多处理机系统。

A real-time system is often used as control de-vice in a dedicated application. 实时系统通常被用作专用的应用的控制设备。

Sensors bring data to the computer. 传感器把数据带给计算机。

The computer must analyze the data and possibly adjust controls to modify the sensor inputs. 计算机必须分析数据,也可能调整控制去修改传感器的输入。

Systems, which control scientific experiments, medical computer systems, industrial control systems, and some display systems are real-time systems. 控制科学的实验,医学的计算机系统,工业的控制系统和一些显示系统等系统都是实时系统。

A real-time operating system has well-defined fixed time constraints.实时操作系统有定义明确的固定的时间约束。

Processing must be done within the defined constraints, or the system will fail. 处理必须在定义的约束中完成,否则系统将失败。

A multiprocessor system has more than one CPU. 多处理机系统有不只一个CPU。

The obvious advantages would appear to be greater computing power and reliability. 显著的优势好像是强大的计算能力和可靠性。

There are various types of operating systems for multiprocessors and multicomputers. 有各种各样的操作系统用于多处理机和多计算机。

It is more or less possible to distinguish two kinds of operating systems for multiple CPU systems: Loosely

coupled, such as network operating system and distributed o/s, and tightly coupled, such as parallel o/s. 这或多或少可能区分两种多CPU系统的操作系统:松耦合,例如网络操作系统和分布式操作系统,和紧耦合,如并行操作系统。

As we shall see, loosely and tightly-coupled s/w is rought analogous to loosely and tight-coupled h/w. 我们应该看到,松紧耦合软件大概类似于松紧耦合硬件。

The operating system must ensure correct operation of the computer system. 操作系统必须确保改正计算机系统的操作。

To prevent user programs from interfering with the proper operation of the system, the h/w was modified to create two modes: user mode and monitor mode[4]. 为了阻止用户程序干扰系统适当的操作,硬件被修改成两种模式:用户模式和监控模式。

Various instructions(such as I/O instructions and halt instructions) are priviledged and can only be executed in monitor mode. 许多指令(例如I/O指令和中断指令)是有特权的,只能在监控模式下被执行。

The memory in which the monitor resides must also be protected from modification by the user. 监控程序所在的内存也必须保护起来以防用户修改。

A time prevents infinite loops. 定时器可以防止死循环。Once these changes (dual mode, privileged instructions, memory protection, timer interrupt) have been made to the basic computer architecture, it is possible to write a correct operating system. 一旦这些对基本计算机体系结构的改变(双模,权限指令,内存保护,定时器中断)被做到,这可能写成一个改进的操作系统。

《计算机专业英语教程》(第4版)

5.1 Internet

因特网

@ Many networks exist in the world, often with different hardware and software.

许多网络通常会以不同的硬件和软件的形式存在于世上。

People connected to one network often want to communicate with people attached to a different one. attached to 附属于

连接了一个网络的人常常想与附属于一个不相同的网络的人交流。

This desire requires connecting together different, and frequently incompatible networks, sometimes by using machines called gateways to make the connection and provide the necessary translation, both in terms of hardware and software.

Desire 心愿 frequently 频繁地 incompatible 不兼容的 in terms of 根据,在???方面

这个要求把不同的和频繁不兼容的网络连接在一起的心愿,有时通过使用叫做网关的机器去构成连接和提供必要的转换,都依据硬件和软件来实现。

A collection of interconnected networks is called an internetwork or just Internet.

A collection of ...的集合 interconnected 互连 internetwork 互连网络 Internet 因特网

互连网络的集合被称为互联网络或只是因特网。

@ A common form of Internet is a collection of LANs connected by a WAN.

一种常见的形式的网络是通过一个广域网连接的局域网的集合。

The Internet(note uppercase I) means a specific worldwide internet that is widely used to connect universities, government offices, companies, and of late, private individuals.

Worldwide 全世界的 note 注意 uppercase 大写字母 internet 互联网 of late 近来

因特网(注意大写字母I)是一个特殊的全世界的互联网,被广泛的用来连接大学,政府部门,公司和近来是私人。

@ By 1995, there were multiple backbones, hundreds of mid-level (i.e. regional) networks, tens of thousands of LANs, millions of hosts, and tens of millons of users.

Backbones 主干网

到1995年,已经有多个主干网,数以百计的中级网络,数以万计的局域网,数以百万计的主机和数以千万计的用户。The size doubles approximately every year.

Approximately 大约

这个大小大约每年翻倍。

Much of the growth comes from connecting existing networks to the Internet.

大部分的增长来自现有网络连接到因特网。

@ The glue that holds the Internet together is the TCP/IP reference model and TCP/IP protocol stack.

Gule 胶水

使因特网在一起的胶水是TCP/IP参考模型和TCP/IP协议栈。

TCP/IP makes universal service possible and can be compared to the telephone system or the adoption of standard gauge by the railroads in the 19th century.

compared to 比喻为 adoption 采用 gauge 轨迹 railroads 铁路

TCP/IP使通用服务成为可能和它可以比喻为电话系统或者在19世纪采用的标准的铁路轨迹。

@ The Internet is a vast global community of real people who constantly generate more unadulterated stuff on more topics than you could ever read in your lifetime.

Vast 广阔的 constantly 不断的 generate 生成 unadulterated 纯粹的 stuff 材料

因特网是现实世界中人们的巨大的全球性社区。在这个网上,人们在众多主题上不断推出的有价值资料是你一辈子也读不完的。

If you haven’t tapped into the yet, here’s what you’re missing:

tapped into 接近挖掘

如果你还没有挖掘到,那么下面就是你所缺少的:

E-mail. Let you send messages to Russia, Japan and so on.

E-mail. 可以让你发送信息到Russia,Japan等等。

File Transfer Protocol (FTP). Download files free of charge from thousands of computers around the globe. free of charge 免费

文件传输协议(FTP)。从全球数以千计的计算机那里免费下载文件。

Usenet newsgroups. More banter, blather, and nuggets of wisdom than you’ll ever be able to read on everything from archery to stock.

Usenet newsgroups 新闻群组 banter 开玩笑 blather 胡说 nuggets 珍闻 archery 箭术 stock 股票

新闻群组。你将可以读到关于从箭术到股票的任何方面的玩笑,胡说和智慧的珍闻。

The World Wide Web(WWW). A fast-growing global network of graphical electronic documents you can browse, interact with, and even create yourself.

fast-growing 高速发展的

万维网(WWW)。一个你可以浏览,交互甚至创建你自己的图像电子文档的高速发展的全球的网络。

New technologies. Global chat, video conferencing, fax, free international phone calls and more. International 国际的

新技术。全球聊天,视频会议,传真,自由的国际电话和更多的。

The World Wide Web 万维网

@ The World Wide Web is an architectural framework for accessing linked documents spread out over thousands of machines all over the Internet.

spread out 传播

万维网是一个用来访问传播在全部因特网中的数以千计的机器中链接的文档的体系结构框架。

Since the Web is basically a client-server system, we discuss both the client (i.e. user) side and the server side.

Basically 基本上 the client side 客户端 the server side 服务器端

由于Web基本上是一个客户-服务器系统,客户端和服务器端我们都讨论。

The Client Side 客户端

@ From the users' point of view, the Web consists of a vast, worldwide collection of documents, usually just called pages for short.

从用户的角度来看,Web由巨大的全世界范围收集的通常简称为页的文件组成。

Each page may contain links (pointers) to other, related pages, anywhere in the world.

每一页可能包含链接到一些在世界任何地方的其他的相关的页面的链接。

Users can follow a link (e.g., by clicking on it), which then takes them to the page pointed to.

用户可以跟踪一个链接(例如,通过点击它),然后带他们到所指向的页面。

This process can be repeated indefinitely, possibly traversing hundreds of linked pages while doing so. Indefinitely 无限期地 traversing 经过

这个处理可以无限重复,当我们那么做,可能经过数以百计的链接页面。

Pages that point to other pages are said to use hypertext.

Hypertext 超文本

指向其他一些页面的页面被称为使用超文本。

Web pages can combine color desktop publishing, hypertext linking, interactive scripting, sound, video,

and even virtual reality.

Combine 组合 publishing 出版

网页可以组合彩色桌面出版,超文本链接,交互脚本,声音,视频甚至虚拟现实。

When hypertext pages are mixed with other media, the result is called hypermedia.

mixed with 与。。。混合 hypermedia 多媒体

当超文本与其他媒体混合,其结果就称为多媒体。

Pages are viewed with a browser.

使用浏览器浏览页面。

The Server Sider 服务器端

@ Every Web site has a server process listening to TCP port 80 for incoming connections from clients (normally browsers).

Incoming 引入的

每个站点都有一个服务进程监听从客户端(通常是浏览器)引入的连接的TCP的80端口。

After a connection has been established, the client sends one request and the server sends one reply. Established 建立

在一个连接已建立,客户端发送一个请求和服务器发送一个回复。

Then the connection is released.

Released 释放

然后连接被释放了。

The protocol that defines the legal requests and replies is called HTTP.

Legal 合法的

那个定义合法的请求和回复的协议叫做HTTP。

A simple example using it may provide a reasonable idea of how Web servers work.

一个使用HTTP的简单例子也许可以提供一个Web服务是如何工作的合理的想法。

Figure 5-1 shows how the various parts of the Web model fit together.

fit together 组装在一起

图5-1显示了Web模式的各个部分是如何组装在一起的。

@ For this example, we can imagine that the user has just clicked on some piece of text or perhaps on an icon that points to the page whose name(URL-Uniform Resource Locator )is http://www.doczj.com/doc/7fe4f2a4b0717fd5360cdc25.html/hypertext/WWW/Theproject.html.

对于这个例子,我们可以想象用户已经点击了指向名为xxx的页面的一些文本或者或许是一个图标。

A URL has three parts:the name of the protocol (http), the name of the machine where the page is located (http://www.doczj.com/doc/7fe4f2a4b0717fd5360cdc25.html) , and the name of the file containing the page (hypertext/WWW/TheProgject.html).

一个URL有三个部分:协议的名称(HTTP),页面所在的机器的名称,和包含了页面的文件名。

The steps that occur between the user's click and the page being displayed are as follows:

Occur 发生

发生在用户点击和页面被显示间的步骤如下:

1The browser determines the URL (by seeing what was selected ).

Deterimines 决定

浏览器决定URL(通过查看那个被选择了)。

2The browser asks DNS for the IP address http://www.doczj.com/doc/7fe4f2a4b0717fd5360cdc25.html.

浏览器向域名服务器要http://www.doczj.com/doc/7fe4f2a4b0717fd5360cdc25.html的IP地址。

3DNS replies with 18.23.0.23.

域名服务器返回18

4The browser makes a TCP connection to port 80 on 18.23.0.23.

浏览器创建一个到18的80端口的TCP连接。

5It then sends a GET /hypertext/WWW/TheProject.html command.

然后它发送一个xx命令。

http://www.doczj.com/doc/7fe4f2a4b0717fd5360cdc25.htmlserver sends the file TheProject.html.

7The TCP connection is released.

8The browser displays all the text in TheProject.html

9The browser fetches and displays all images in TheProject.html.

Fetches 获取

Surfing the Web 网络冲浪

@ Once your Web browser is open and you are connected to the Internet, the page currently designated as your browser's starting page or home page will be displayed within the browser window.

Designate 指定

一旦你的网络浏览器打开然后你连接到了因特网,那个当前指定为你浏览器起始页或者首页的页面将会在浏览器窗口中显示。

(Usually this page is the home page for your browser's, school's , or ISP's Web site, but it can usually be changed to any page using your browser's Options or Preferences dialog box.)

(通常这页是你的浏览器的,学校的,因特网服务提供商的网络站点,但是你可以使用你的浏览器的选项或者偏爱对话框来改变成任何页面。)

@ All browsers have navigational tools to help you move forward or backward through the pages viewed in your current Internet session, as well as buttons or menu options to print Web pages when necessary. Navigational 引导的

所有的浏览器都有导航工具来帮助你在你当前的因特网会话中向前或者向后查看页面,同样也有用来打印当需要时的网络页面的按钮和菜单选项。

Figure 5-2 illustrates the most common components of the Microsoft Internet Explorer and Netscape Navigator browsers.

图5 – 2举例说明微软Internet Explorer和网景航海家浏览器的最常见的组成部分。

Using URLs and Hyperlinks 使用URL和超链接

@ To change from the starting Web page to a new Web page, you can type the appropriate URL in the browser's address bar or location bar and press Enter.

Type 输入

为了从起始页转到一个新的页面,你可以在浏览器的地址栏和本地栏中输入一个合适的URL,然后按下回车键。

You can either edit the existing URL or delete it and type a new one.

你既可以编辑存在的URL也可以删除它然后输入一个新的。

Be sure to match the spelling, capitalization, and punctuation exactly.

Spelling 拼写 capitalization 大写 punctuation 标点

一定要准确的匹配拼写,大写和标点。

If you don’t know the appropriate URL to type, you can search for an appropriate page, as discussed shortly.如果你不知道合适的URL要输入,你可以搜索一个合适的页面,如不久前讨论的。

@ If there is a hyperlink displayed for the page you would like to go to, simply click on the link. 如果这里有一个显示了你想要去的页面的链接,简单点击链接即可。

Remember, hyperlinks can be either text or image-based.

记住,超链接既可以是文本也可以是基于图像的。

If you are not sure if something on a page is a link or not, rest the mouse pointer on it for a moment. 如果你不确定在页面上的东西是链接或者不是,让鼠标指向它一段时间。

If it is a hyperlink, the pointer should change to indicate that it is a link.

Indicate 表明

如果它是一个链接,那么指针会改变,这表明它是一个链接。

The URL for the new page is also displayed on the browser's status bar.

新页面的URL也会显示在浏览器的状态栏。

Once you click the hyperlink, the appropriate page is displayed.

一旦你点击了超链接,合适的页面被显示。

To return to a previous page, click the Back button on your browser's toolbar.

为了回到先前的页面,点击在浏览器上的工具条中的返回按钮。

To print the current Web page, use browser's Print button or select Print from the browser's File menu. 为了打印当前的网页,使用浏览器的打印按钮或者从浏览器的文件菜单中选择打印。

Things You May Encounter on a Web Page 在网页上你将遇到的东西

@ You will encounter a variety of different objects on Web pages as you explore the World Wide Web. Explore 浏览

当你在浏览万维网时,你将在网页上遇到各种各样的不同的对象。

Though we can’s go into an in-depth discussion on the various possible Web-page components here, it is

good to be a familiar with the most common ones so you'll know how to deal with them as you encounter them. 在这里,尽管我们不能对各种可能的网页组件进行深入的讨论,最好是对大部分的组件都熟悉,这样你就能知道当你遇到它们时如何处理它们了。

Some common things you may run into are illustrated in Figure 5-3.

在图5-3中举例说明了一些你也许会遇到的常见的东西。

《计算机专业英语教程》(第4版)

5.2 Type of Connection

连接类型

@ As discussed in the previous chapter, there are a variety of wired and wireless ways to connect to the Internet.

wired 有线的 wireless 无线的

正如前面章节讨论的,有各种各样的的有线的和无线的方式来连接到因特网。

In virtually all setups, the computer to which you connect is usually connected to a large network called a regional network; regional networks are connected to the major high-speed networks within each country called backbone networks.

virtually 事实上 setups 设置

事实上所有的设置,你所连接的计算机通常连接到一个叫做区域网的巨大的网络;区域网又连接到叫做主干网的在每个国家内部的主要高速网络。

Backbone networks within a country are connected to the major high-speed networks within ecah country called backbone networks.

一个国家中多个主干网连接到每个国家中的主要高速网络称为主干网。

Backbone networks within a country are connected together and to backbone networks in other countries to form the Internet.

一个国家中的多个主干网的连接及与其他国家中的主干网的连接就形成了因特网。

@ The following sections discuss the most common types of Internet connections.

下面部分讨论了大部分常用的因特网连接类型。

1.Dial-Up Connections 拨号连接

@ Dial-up connections usually work over regular telephone lines.

regular 正规的

拨号连接通常工作在正规的电话线。

To connect to the Internet, your modem (or other appropriate interface device ) dials up and connects to a modem attached to your ISP's computer..

modem 调制解调器

为了连接到因特网,你的调制解调器(或其他适当的接口设备)拨号然后连接到附属于你的因特网服务提供商的计算机的调制解调器。

While you are connected, your PC is assigned a temporary IP address for the current session.

当你连接上了,你的电脑被指派一个用于当前会话的临时的IP地址。

At the end of each Internet session, you disconnect from your ISP's computer to allow another user to connect in your place.

disconnect 断开一个网络连接

在每一次因特网会话结束时,你从你的因特网服务提供商的计算机上断开一个网络连接以允许处于你位置的其他用户去连接。

One advantage to a dial-up connection is security.

拨号连接的一个优势是安全。

Since you are not continually connected, it is much less likely that anyone would gain access to your computer via the Internet, to either obtain information or mess with the data on your PC or, more commonly, to user your computer in some type of illegal or unethical manner.

via 经由 mess with 搞糟打扰 illegal 非法的

因为你不持续地连接,所以不大可能有人能经由因特网获得你计算机的访问,或者获得你的PC上的信息或者搞糟电脑的数据,或者更常见的是以某种不合法或者不道德的方式使用你的计算机。

These types of hacking activities are discussed later.

hacking 黑客行为

这些不同类型的黑客行为活动后面将讨论。

@ With a dial-up connection your telephone will be tied up while you are accessing the Internet, unlesss a second phone line is used.

tied up 被占用

使用拨号连接,当你正在访问因特网时你的电话将被占用,除非第二条电话线被使用。

Some Internet call-waiting or call-forwarding services allow you to be notified when you get a telephone call while you are connected to the Internet.

call-waiting 呼叫等待 call-forwarding 自动转接

在你连接了因特网期间,当来了一个电话呼叫时,一些因特网呼叫等待或者自动转接服务会通知你。

They are generally set up to allow the person to leave a short message;

它们通常设置允许人们留下一个简答的信息。

some newer systems give you a short window of time to disconnect from the Internet and pick up the telephone call, if desired.

一些新的系统给你一个较短的时间从因特网上断开然后拿起电话,如果你愿意。

Newer dial-up modems are expected to facilitate some type of call-waiting service, as well.

facilitate 促进

新的拨号调制解调器被期望来促进某种类型的呼叫等待服务。

Standard Dial-up 标准拨号

@ Standard dial-up Internet service uses a conventional dial-up modem rated at a maximum data transfer rate of 56 Kbps.

标准拨号因特网服务使用一个最大数据交换数度是56Kbps的传统的拨号调制解调器。

These modems are commonly used with PCs and Internet appplicances.

这些调制解调器通常用于PCs和因特网应用。

Portable devices may also use a conventional dial-up modem; if so, they need to be connected to standard telephone jacks to access the Internet.

Portable 便携的 jacks 插座

便携的设备也使用传统的拨号调制解调器,假如这样,他们为了访问因特网需要连接到标准的电话插座上。

Standard dial-up Internet service range from free to about $ 25 per month.

标准的拨号因特网服务从免费到大约每个月25的范围内。

ISDN 综合业务数字网

@ Another dial-up option is ISDN.

另外一个拨号选择是综合业务数字网。

ISDN(integrated services digital network) allows digital transmission of data over ordinary telephone lines. transmission 传输

综合业务数字网允许通过不同的电话线进行数据的数字传输。

It requires a special ISDN adapter or modem and can transfer data up to 128 Kpbs.

它需要一个特殊的ISDN适配器或者调制解调器,可以传输数据达到128Kbps。

2. Direct Connections 直接相连

@ Unlike dial-up connections that only connect to your ISP's computer when you need to access the Internet, direct connections keep you continually connected to the Internet.

不像拨号连接那样,当你需要访问因特网时,只能连接到ISP的计算机上,直连使得你可以持续连接到因特网。

With a direct (always-on) connection, your PC is typically issued a static (nonchanging) IP address to be used to transfer data back and forth via the Internet.

issued 发布

通过直连,你的PC典型的发布一个用于经由因特网来回交换数据的静态IP地址。

PCs connected to the network always have an Internet connection available-Internet access requires only opening a browser.

电脑连接到网络总是有一个因特网连接可能的网络访问只需要打开一个浏览器。

@ Types of direct Internet connections include connecting through a school or office LAN, as well as DSL, cable, satellite, and fixed wireless connections.

Cable 电缆 satellite 卫星

直接的因特网连接类型包括通过一个学校或者政府机关的局域网以及数字用户线,电缆,卫星和固定无线连接进行连接。

Though, in theory, broadband Internet access can be up to 100 times as fast as a dial-up connection, actual

speeds at the present time are more like 25 to 50 times as fast.

Theory 理论 broadband Internet access 宽带上网

虽然,在理论上,宽带上网可以快速到拨号连接的100倍,实际现在的速度则更像是25到50倍。

Typical download speeds for DSL and cable are about 1.5 Mbps;

数字用户线和电缆的典型地下载速度大约是1.5Mbps。

satellite and fixed wireless usually download data between 500 Kbps to 1 Mbps.

卫星和固定无线通常下载数据在500Kbps到1Mbps之间。

Virtually all of these services use slower upload speeds.

几乎所有这些服务使用较慢的上传速度。

The most significant characteristics of each of these types of broadband Internet access are discussed next. 每一种这些宽带上网的类型的最重要的特点将在后面讨论。

School or Office LAN

@ Most school or office LANs that offer a direct connection to the Internet lease a high-speed dedicated line (such as an ISDN or T1 line) from the telephone company or an Internet provider.

lease 租约 dedicated 专用的

大多数学校或者政府机关的局域网,提供一个与因特网直接相连的从电话公司或者因特网提供者那里租约一条高速专用线。

The speed of this type of Internet access depends on the speed of the connection between the school or offices and their Internet provider, as well as the speed of the LAN itself.

这种类型的因特网接入速度依赖学校或者政府机关和它们的因特网提供者间的连接速度,同样也依赖于局域网本身的速度。

DSL

@ DSL (digital subscriber line) is currently available only to users who are relatively close (three miles or less ) to a telephone switching station with telephone lines capable of handling DSL, and long waits for installation are not uncommon.

subscriber 用户 capable 有能力的

DSL目前只对那些较靠近电话交换站(3英里或小于3英里),有能力处理DSL电话线的用户可用,并且常要等很长时间安装。

Nevertheless, DSL is a popular broadband option.

Nevertheless 然而

然而,DSL是一项很受欢迎的宽带的选择。

DSL is sometimes offered at different speeds to fit different needs and budgets, such as a slower, less-expensive personal version and a faster business option.

Budgets 预算

DSL有时提供不同的速度以满足不同的需要和预算,例如慢速低价的个人版本和快速的商业选择。

The monthly cost of standard DSL service is about $50.

标准DSL的每月消费大约是50美元。

Cable 电缆

@ A third type of direct Internet connection-cable-is the most widely used home broadband alternative. Alternative 供选择的

第三种因特网直连类型是电缆,它是最广泛使用的家庭宽度选择。

Cable connections are very fast and are available to anyone with cable access whose cable provider has upgraded the system to support Internet access.

upgraded 升级

电缆连接是相当快的,可以让任何人通过电缆访问,电缆提供商升级了支持因特网访问的系统。

Just about all cable Internet access today is two-way (full-duplex), with the cable being used to transfer data in both directions.

今天几乎所有的电缆因特网访问是双向的(全双工),通过在两个方向上用来交换数据的电缆。

One disadvantage of cable is that all users in an immediate geographical area share the bandwidth of their local cable.

电缆的一个劣势是在邻近地区的所有用户共同使用他们本地电缆的带宽。

Though this may not prove to be a problem all the time, during high-use times of day--such as early evening--the speed of cable Internet service can slow down dramatically as your neighbors go online.

dramatically 戏剧的

尽管这并不能证明是一个问题,在一天的高使用时间电缆因特网服务的速度会变低,戏剧的你的邻居上线了。

Cost is about $40 per month, in addition to regular cable fees.

in addition to 除...之外 fee 费用

费用大概是每月40美元,除了常规的电缆费用外。

Satellite 卫星

@ Satellite Internet access is often the only broadband option in rural areas.

rural 农村的

卫星因特网访问是在农村地区唯一的宽带选择。

It requires a satellite modem and a transceiver satellite dish mounted outside the home or building. transceiver 收发器 dish 蝶形天线 mounted 安装

它需要人造卫星调制解调器和安装在室外或建筑物外的收发卫星蝶形天线。

The two-way satellite services available today, such as StarBand, are relatively reliable, though an unobstructed view of the southern sky is requited and access may degrade very heavy rainstorms.

虽然需要在蝶形天线收发方向的上空没有任何障碍,并且在大暴风雨期间访问性可能降低,但目前可用的两路人造卫星服务,如StarBand,是相当可靠的。

Typical cost is about $70 per month.

典型的费用大约是每月70美元。

Fixed Wireless 固定无线

@ One last type of broadband access that is relatively new for consumer use but shows great promise is fixed wireless.

最后一种宽度访问是固定无线,这种访问方式对消费者使用是相当新的,但显示出很大的前途。

This type of service, such as Sprint Broadband Direct, is similar to satellite service in that it requires a modem and an outside-mounted transceiver, but is typically available only in larger metropolitan areas. metropolitan 大都市的

这种服务的类型,例如Sprint Broadband Direct,像卫星服务一样需要一个调制解调器和一个外部安装的收发器,但通常只有在大的大城市地区。

A clear line-or-sight is required between the transceiver and the provider's radio transmission tower, which relays information between the user's transceiver and the Internet.

radio 无线电广播 tower 塔 relays 中继转播

在收发器和提供商的无线传输塔之间需要有一条无障碍的视线通路,传输塔在用户的收发器和Internet间转播信息。Cost for service is about $50 per month.

这种服务的费用大约是每月50美元。

@ Regardless of the type of connection used, a very important consideration for all users with a direct Internet connection is protecting the computer from unauthorized access or hackers.

Regardless of 不管 unauthorized 未经授权的

不管那种类型的连接被使用,对所有直接连接到因特网的用户一个非常重要的考虑是保护计算机不受未经授权的访问或者黑客的攻击。

While most schools and offices are protected by some type of firewall, many home direct connections are not.

然而大多数学校和政府机关通过一些防火墙来保护,许多直接连接的家庭则不是。

Though it is unlikely that someone would access your home PC in this manner, the possibility will continue to increase as direct home connections become more common.

尽管不大可能有人访问你家的电脑用这种方式,直接连接回家的可能性将持续增长也变得更加普遍。

To protect yourself, all computers using a direct connection should use a personal firewall program--especially those on a home network that allows file sharing.

especially 尤其

为了保护你自己,所有使用了直连的计算机可以使用个人防火墙程序--尤其是那些允许文件共享的家庭网络的计算机。Firewall programs typically block access to your PC from outside computers, as well as allow you to specify which programs on your PC can access the Internet.

block 阻止 specify 指定

防火墙程序典型地阻止从外部来的一些计算机去访问你的电脑,同样也允许你指定在你计算机上的那些程序可以访问因特网。

Some firewall software, such as the Zone Alarm software, are available free for home use.

一些防火墙软件,例如Zone Alarm软件,对家庭可以免费使用。

Some firewall protection is beginning to be incorporated into other programs, such as Windows XP. incorporated 包含

一些防火墙保护开始纳入其他程序,如Windows XP。

3. Mobile Wireless Connections 移动无线连接

@ Unlike satellite and fixed wireless connections, which use a cable to connect the modem to some type of fixed transceiver, mobile wireless connections allow the device to be moved from place to place.

不像卫星和固定的无线连接,使用电缆去连接调制解调器或一些固定收发器,移动无线连接允许设备从一个地方移动到另一个地方。

Consequently, most handheld PCs and other mobile devices (like Web-enabled cell phones) use a mobile wireless connection and access the Internet through the same wireless network as cell phones and messaging devices. Consequently 因此 cell 电池细胞

因此,大部分手提电脑和其他移动设备(像能用Web服务的手机)使用移动无线连接然后通过同样的无线网络如手机和通信设备访问因特网。

Most mobile phones today capable of Internet access come "wireless Internet-ready" and can immediately be used to retrieve Web content, provided wireless Web service is included in the phone's service plan. retrieve 检索

现在大多数能访问Internet的移动电话都处于无线Internet就绪状态并且能直接用来检索Web内容,只要提供的无线Web服务包括在该手机的服务计划中。

Many handheld PCs also have Internet connectivity built in; if not, a wireless modem can be used.

许多手提电脑也可以建立有互联网的连接;如果不能,可以使用一个无线调制解调器。

Alternately, a modem or other type of adapter can connect the device to a cell phone.

Alternately 交替地

交替地,一个调制解调器或者其他类型的适配器可以连接设备到手机。

Notebook PCs can connect to the Internet or a corporate network using either a wireless modem or cell modem. corporate 公司的 cell modem 细胞调制解调器

笔记本电脑使用无线调制解调器或者细胞调制解调器可以连接到因特网或者一个公司的网络。

Some notebook computers today come with wireless capability built into the unit.

come with 伴随 built into 固定于

现在的一些笔记本电脑伴随有固定了无线能力的单元。

《计算机专业英语教程》(第4版)

6.2 Carrier Frequencies and Multiplexing

载波频率和多路复用

@ Computer networks that use a modulated carrier wave to transmit data are similar to television stations that use a modulated carrier wave to broadcast video.

modulated 已调制的

使用调制载波发送数据的计算机网络和利用调制载波广播视频信息的电视台相类似。

The similarities provide the intuition needed to understand a fundamental principle:

similarity 相似性 intuition 直观

这一相似性给理解下述基本原理提供了启示:

Two or more signals that use different carrier frequencies can be transmitted over a single medium simultaneously without interference.

signal 信号 simultaneously 同时地 interference 干扰

两个或多个使用不同载波频率的信号可以在单一介质上同时传输而互不干扰。

@ To understand the principle, consider how television transmission works.

为理解这一原理,考虑(有线)电视传输是如何工作的。

Each television station is assigned a channel number on which it broadcasts a signal.

channel 频道

每个电视台都分配一个频道号,它在该频道上广播信号。

In fact, a channel number is merely shorthand for the frequency at which the station's carrier oscillates. shorthand 速记 oscillate 振荡

事实上,频道号就是电视台载波用的振荡频率的速记。

To receive a transmission, a television receiver must be tuned to the same frequency as the transmitter.

tune to 调谐到

为接收一个频道传输,电视接收器必须调谐到与发送器相同的频率。

More important, a given city can contain many television stations that all broadcast on separate frequencies simultaneously.

更重要的是,一个城市可以有许多电视台,它们彼此在不同的频率上同时广播。

A receiver selects one to receive at any time.

一个接收器在任一时间选择接收其中一个。

@ Cable television illustrates that the principle applies to many signals traveling across a wire.

有线电视这一例子说明了以上原理应用于许多信号在一根导线上同时传输的情况。

Although a cable subscriber may have only one physical wire that connects to the cable company, the subscriber receives many channels of information simultaneously.

虽然一个有线电视用户可能只有一根线连向有线电视公司,但用户可同时收到许多频道的信息。

The signal for one channel does not interfere with the signal for another.

一个频道中的信号不会与另一频道中的信号相互干扰。

@ Computer networks use the principle of separate channels to permit multiple communications to share a single, physical connection.

permit 允许

计算机网络使用分离频道的原理使多个通信共享单根物理连线。

Each sender transmits a signal using a particular carrier frequency.

每个发送器使用一个特定载波频率传输信号。

A receiver configured to accept a carrier at a given frequency will not be affected by signals sent at other frequencies.

一个接收器被设置成接收给定频率的载波,它将不会受其它频率信号的影响(或干扰)。

All carriers can pass over the same wire at the same time without interference.

所有载波可在同一时间通过同一导线而互不干扰。

Frequency Division Multiplexing 频分多路复用

@ Frequency division multiplexing(FDM) is the technical term applied to a network system that uses multiple carrier frequencies to allow independent signals to travel through a medium.

频分多路复用(FDM)是使用多个载波频率在一个介质中同时传输多个独立信号的计算机网络系统术语。

FDM technology can be used when sending signals over wire, RF, or optical fiber.

当通过导线、RF或光纤发送信号时便可使用FDM技术。

Figure 6-1 illustrates the concept, and shows the hardware components needed for FDM.

图6-1说明了这一概念并显示了FDM所需的硬件部件。

@ In theory, as long as each carrier operates at a different frequency than the others, it remains independent.

理论上,工作在不同频率上的载波将保持相互独立。

In practice, however, two carriers operating at almost the same frequency or at exact multiples of a frequency can interfere with one another.

但实际上,两个频率相近或频率成整倍的载波会彼此干扰。

To avoid problems, engineers who design FDM network systems choose a minimum separation between the carriers. 为了避免这些问题,设计FDM网络系统的工程师们在各载波之间选择一个最起码的频率分隔。

The mandate for large gaps between the frequencies assigned to carriers means that underlying hardware used with FDM can tolerate a wide range of frequencies.

mandate 授权 underlying 相关的 tolerate 容纳

在各载波频率之间要求有较大的间隔意味着FDM所用的相关硬件能容纳很宽的频率范围。

Consequently, FDM is only used on high-bandwidth transmission channels.

因此,FDM仅用于高带宽传输通道中。

In summary, 概括地说,

Frequency division multiplexing(FDM) allows multiple pairs of senders and receivers to communicate over a shared medium simultaneously.

频分多路复用允许多对发送和接收装置在一个共享介质上同时通信。

The carrier used by each pair operates at a unique frequency that does not interfere with the others.

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