题目内容
（请给出正确答案）
A computer virus plagues other computers by ______.
A．misguiding the header information at the beginning of the file
B．preying on other computer files
C．attaching its infected code to the end of a host program
D．all of the above
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| The problem was settled to the complete____of them, so they didn't complain. |
[ ] |
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Software Security
软件安全
We live in a world today where software is pervasive. Software touches nearly every aspect of our lives, from software-controlled subways, air traffic control systems, nuclear power plants, and medical equipment to more mundane everyday examples, such as software-controlled microwave ovens, gas burners, elevators, automated teller machines[1], the family car, and the local 911 service[2]. In the past, many of these items relied upon established safety and reliability principles from electrical, mechanical, and/or civil engineering, which developed over several decades, if not longer. Today items like these are controlled by software.
When it is examined, its totality, the magnitude of the software safety and reliability challenge facing us today makes the Y2K[3]problem look minuscule by comparison. Hence, it is time to acknowledge the discipline of software safety and reliability and its importance to everyday life. Some people and organizations are starting to understand and respond to this challenge. For example, the FBI[4]recently established a National Infrastructure Protection Center to protect safety-critical systems and software. Unfortunately, many still remain blissfully unaware of the situation or deny its existence. Contributing to the problem is the small number of universities that offer courses in software safety and reliability.
We hear a lot about the global economy today. Technology has less respect for state or national borders than do market forces. The software safety and reliability challenge is a global challenge. Products, such as cars and medical devices, are built in one jurisdiction and sold worldwide. Air traffic control systems must interoperate safely and reliably among multiple countries, for example along the long borders between the U. S. , Canada, and Mexico. Accordingly, the first part of this book introduces the concept of software safety and reliability, and techniques and approaches used to achieve and assess it.
Background
The inherent complexity of software—its design, development, assessment, and use—is and has been increasing rapidly during the last decade. The cycle time between new versions of system and application software has decreased from a number of years to a number of months. The evolution and discovery of new design techniques and development methodologies are proceeding at an equally rapid pace. Consequently, the debate about what constitutes the standard body of knowledge for Computer Science professionals continues.
Accompanying this is the ever broadening role that software plays in electronic products. A study performed in the U. K. in 1990 estimated that the market for the development of safety-related software was ＄. 85B per year and that it was growing at a rate of 20 percent per year. This is due to the fact that software is replacing discrete hardware logic in many devices. Some common examples include air traffic control systems, nuclear power plant control systems, and radiation therapy systems. In addition, advanced electronics with embedded software controllers are being incorporated into a variety of new products, such as laser surgical devices, automobiles, subways, and intelligent transportation systems.
As such the role of software has moved from simply generating financial or other mathematical data to monitoring and controlling equipment, which directly affects human life and safety. In fact, it was reported by Donald Mackenzie that "the total number of people killed by computer system failures, worldwide, up to the end of 1998 is between 1,000 and 3,000. "
As a result, a more thorough and widespread understanding of, and familiarity with the specialized techniques to achieve and assess the safety and reliability of software, are needed in academia, industry, and government. This is also true since many legal issues related to software liability are evolving.
Purpose
While the general concept of safety and reliability is understood by most parties, the specialty of software safety and reliability is not. The understanding of electronic component reliability and electrical safety has been evolving since the 1940s. In contrast, software safety and reliability is a relatively new discipline that only a few understand well or at all. Hence, the overall goal of writing this book is to improve the state of the art of software safety and reliability, both its understanding and practice. This goal is achieved through three objectives.
The first objective of this book is to serve as a "consciousness raising"[5]about the importance of software safety and reliability and the attention this subject warrants in mission critical systems[6]. As more and more functionality is shifted from hardware to software, two common scenarios occur. First, managers and technical personnel involved in mission critical projects are generally very knowledgeable about optics, radiation physics, mechanical engineering, and so forth. However, they are sometimes at a loss when it comes to knowing: 1) what to do about software safety and reliability; 2) the skill set that is needed to adequately address software safety and reliability; and 3) sometimes even that this subject warrants serious attention. Second, today there are many excellent Computer Science and Software Engineering programs at universities throughout the worlＤ. Unfortunately, very few of them offer any courses on software safety and reliability or on software engineering standards. A student may acquire a thorough background in software engineering without being exposed to the field of software safety and reliability. Given the shift in technology to software controlled products, this is unfortunate because today's students will be tomorrow's safety and reliability practitioners. This book has been written to serve as a "consciousness raising" for both scenarios. As such, it includes many illustrative everyday examples about the importance of software safety and reliability.
The second objective of this book is to provide practical information about the current methods used to achieve and assess software safety and reliability. This is accomplished by a comprehensive discussion of the current approaches promoted by key industrial sectors and standards organizations to software safety and reliability. Since most practitioners were not taught software safety and reliability in school, it is all the more imperative that they be made aware of current software safety and reliability standards[7]. As a rule, standards are written in a very terse style. A phrase or sentence may be very meaningful to the committee members who spent years writing the standard, but the same phrase leaves the average reader in the dark. Accordingly, Parts Ⅱ and Ⅲ of this book have been written in the style of an application guide—" how to" read, interpret, and implement a given standarＤ. While theory is not entirely neglected, the emphasis is on practical information.
The third and final objective of this book is to bring together, for the first time, in one volume the contemporary thinking on software safety and reliability so that it can be compared and analyzed; thereby leading to the improved understanding and practice of this field in the future.
Firewall
Nations without controlled borders cannot ensure the security and safety of their citizens, nor can they prevent piracy and theft. Networks without controlled access cannot ensure the security or privacy of stored data, nor can they keep network resources from being exploited by hackers.
The communication efficiency provided by the Internet has caused a rush to attach private networks directly to it. Direct Internet connections make it easy for hackers to exploit private network resources. Prior to the Internet, the only widely available way for a hacker to connect from home to a private network was direct dialing with modems and the public telephone network. Remote access security was a relatively small issue.
When you connect our private network to the Internet, you are actually connecting your network directly to everv other network attached to the Internet. There's no inherent central point of security control.
Firewalls are used to create security checkpoints at the boundaries of private networks. By providing the routing function between the private network and the Internet, firewalls inspect all communications passing between the two networks and either pass or drop the communications depending on how they match the programmed policy rules. If your firewall is properly configured and contains no serious exploitable bugs, your network will be as free from risk as possible.
Firewalls are among the newest developments in Internet technology. Developed from rudimentary security systems that major computer vendors like Compact and IBM developed to secure their own networks in the mid 1980s, these network sentinels have developed in lock-step with the burgeoning threat of information warfare. The most interesting and innovative developments, like Network Address Translation and multi-layer security filtering, are so new that books just two years old are already obsolete.
The security problems of the past could be solved with simple packet filters and dial- back modem banks. The security problems of the future will require rifling through and validating every byte of an Internet message, requiring encrypted certification of a web site's true identity before connecting, and then encrypting nearly everything that travels between. Fortunately, as technology and the technological society it mirrors progress, these measures will become simple and invisible. As vendors make operating systems more hardened against attack, the World Wide Web will secretly grow more secure for people who will freely surf the Web as they please, hampered only by the occasionally warning that a site is not accredited or that a message contains suspicious content. This is as it should be.
The security problems of today are most effectively solved with firewalls and virtual private tunnels. Peripheral security utilities[8]like intrusion detectors and security scanners do their part to alarm and alert, but firewalls will remain the foundation of Internet security until their functionality is built into the very protocols upon which the Internet operates and until every Internet-connected computer contains the equivalent of a firewall. Even then, centralized management of Internet policy may make firewalls a permanent addition to corporate networking.
Notes
[1]automated teller machines：自动取款机，简写成ATM。
[2]911 service：在美国等一些西方国家，紧急救护号码为9ll。
[3]Y2K(Year 2000)：电脑千年虫。
[4]the FBI：(美国)联邦调查局(Federal Bureau of Investigation)的缩写。
[5]consciousness raising：提高意识。
[6]mission critical systems：任务是至关重要的系统。
[7]It is...从句中用should+do，should常可省，如：It is important that he start early tomorrow.
[8] Peripheral security utilities: 外围(部)安全设备。
Choose the best answer:
A．No firewall contains serious exploitable bugs.
B．Your computer can't work without a firewall.
C．Direct Internet connections provide hackers with an easy way of invasion.
D．Firewalls need no configuration.
A．it is reliable
B．it runs fastest
C．it gives the best price/performance ratio
D．it works as a single computer
A．a sudden loud noise B．benefit
C．a group of computers D．performance
A．tell us what a commercial distributed system is
B．state that a distributed system is more useful than a centralized one
C．explain why management runs its supermarket chain with a distributed system
D．give reasons why a distributed system is used in a supermarket chain
A．what a distributed system is
B．advantages of distributed systems over centralized systems
C．the development of the distributed system
D．the wide application of distributed systems
Computer Office System
计算机办公系统
Computer office systems are computers and their peripheral equipment is used to create, store, process, or communicate information in a business environment. This information can be electronically produced, duplicated, and transmitted.
The rapid growth of the service sector of the United States economy beginning in the mid 1970s has furnished a new market for sophisticated office automation. With the increasing incorporation of microchips and microcircuitry into office equipment[1], the line between the computer and other equipment has blurred.
At the same time, computers either stand alone or as part of a network and specialized software programs are taking over tasks such as facsimile transmission-or FAX, voice mail, and telecommunications that were once performed by separate pieces o.f equipment. In fact, the computer has virtually taken the place of typewriters, calculators, and manual accounting techniques and is rapidly taking over graphics design, production scheduling, and engineering design as well.
During the first half of the 20th century, financial and other numerical record keeping tasks were performed manually or by bookkeeping machines, billing machines, tabulating equipment, and other types of electromechanical accounting devices. In the 1950s, such machines were increasingly replaced by mainframe computers-large, very expensive, high speed machines that required trained operators as well as a special temperature regulated facility to prevent overheating. Use of these machines today is limited to large organizations with heavy volume data processing requirements. Time sharing, allowing more than one company to use the same mainframe for a fee, was instituted to divide the cost of the equipment among several users while ensuring that the equipment is utilized to the maximum extent.
Mainframes with remote terminals, each with its own monitor, became available in the mid 1970s and allowed for simultaneous input by many users. With the advent of the minicomputer, however, a far less expensive alternative became available. The transistor and microelectronics made manufacture of these smaller, less complex machines practicable. Minicomputers, the first of which entered general business use in the early 1960s, are now widespread in commerce and government. Terminals linked to the central processing unit (CPU) are under the direct control of the individual user rather than centralized staff. In recent years, however, it is the microcomputer, or personal computer (PC), that has come to play the principal role in most office workplaces.
Desktop PCs have become increasingly affordable as a result of industry wide adoption of the architecture of the PC introduced in 1981. Although it has become feasible to provide virtually every office worker with a PC, it is more cost effective for PC users to share files and common peripherals such as printers, facsimile boards, modems, and scanners. In the late 1980s and early 1990s, many companies began programs of linking or networking multiple PCs into a unified system.
The local area network (LAN) was created in response to the need for a standardized system of linking computers together in a company. The most common method used to connect computers to a network is by means of coaxial cables. Newer generation networks use fiber optical connections. When computers are not in close physical proximity, networks may use microwave radio or infrared radiation to link the computers. Microwave radio requires a dish antenna for transmission and reception; infrared radiation requires a lens for transmission and a mirror and lens for reception. Other methods used for wide area networking include telephone and communications satellite linkage.
The need for computer connectivity has established the usefulness of the peripheral device known as the modem. Modems permit two computers to communicate by telephone in order to access databases, transmit files, upload and download facsimile transmissions, and send and receive electronic mail. Early transmission speeds using this equipment were relatively slow—300 baud[2]. Some modems now operate at speeds of more than 50,000 baud and have error checking and data compression features.
Text materials in typed or printed form can be input directly into a computer by means of a scanner. To read text, optical character recognition (OCR) software must first be used to convert printed documents electronically into computer readable files. Scanners obviate the need to rekey printed text in order to input it; they can also be used to input graphic material.
Computer Printers
A considerable volume of office computer output is via the printer. Among the earliest printers used with PCs in business offices were daisy wheel and thimble printers, so called because of the shape of their printing elements[3]. Although their type quality was comparable to that of a typewriter, they were slow and could accommodate only text, not graphic materials. As a result, they have been supplanted in most offices by dot-matrix, ink jet, and laser printers.[4]The dot matrix printer may have a 9 or 24 pin print head. The pins impact the paper through a ribbon, creating patterns of dots in the shape of letters and numbers in multiple fonts and type sizes. The ink jet printer, an advance over the dot matrix, provides both high resolution (the higher the resolution, the better the print quality) and quiet operation. The laser printer represents an even greater advance. Similar in technology to a photocopier[5], it offers speed, high resolution of 300 dots or more per inch, ability to reproduce complex graphics, and silent operation—all of which make it virtually essential for desktop publishing.
Electronic Mail (E-mail)
E-mail has become a key part of the communication networks of most modern offices. Data and messages can be transmitted from one computer to another using telephone lines, microwave links, communications satellites, or other telecommunications equipment. The same message can be sent to a number of different addresses. E-mail is sent through a company's own LAN or beyond, through a nationwide or worldwide communications network. E-mail services use a central computer to store messages and data and to route them to their intended destination. With a subscription to a public E-mail network, an individual PC user needs only a modem and a telephone to send and receive written or vocal messages. Because of the huge amount of E-mail that can be generated, systems have been developed to screen mail[6]for individual users.
Voice Mail
A specialized type of E-mail system, voice mail, is a relatively simple, computer linked technology for recording, storing, retrieving, and forwarding phone messages. It is called voice mail, or voice messaging, because the messages are spoken and left in a voice mailbox. The telephone doubles as a computer terminal, but instead of presenting the information on a computer screen, the system reads it over the phone line, using prerecorded voice vocabulary. The systems are based on special purpose computer chips and software that convert human speech into bits of digital code. These digitized voices are stored on magnetic disks, from which they can be instantaneously retrieved. Callers are offered a menu of choices, and the messages they select are played; they can leave messages in voice mailboxes, or they can access huge computer databases.
Desktop Publishing
Desktop Publishing is the use of a computer and specialized software to combine text and graphics to create a document that can be printed on either a laser printer or a typesetting machine. Desktop publishing is a multiple step process involving various types of software and equipment. The original text and illustrations are generally produced with software such as word processors and drawing and painting programs and with photograph scanning equipment and digitizers. The finished product is then transferred to a page makeup program, which is the software most people think of as the actual desktoppublishing software. This type of program enables the user to lay out text and graphics on the screen and see what the results will be: for refining parts of the document, these programs often include word processing and graphics features in addition to layout capabilities. As a final step, the finished document is printed either on a laser printer or, for the best quality, by typesetting equipment.
Notes
[1] With the increasing incorporation of microchips and microcircuitry into office equipment: incorporation of sth. into sth. else = to incorporate sth. into sth. else, 意为“将……结合进……”。本句可译为：随着微型芯片和微型电路越来越多地进入办公设备，计算机与其他设备之间的界线已不那么分明了。
[2] baud：波特(通信中的符号传输速率单位，每秒传输一个符号称为1波特)。
[3] Among the earliest printers used with PCs in business offices were daisy wheel and thimble printers, so called because of the shape of their printing elements．本句为倒装句，原句应为：Daisy wheel and thimble printers were among the earliest printers used with PCs in business offices... "so called" 为形容词，引出状语，表示伴随情况，对主语进一步说明。
[4] dot-matrix, ink jet, and laser printers：点阵，喷墨，激光打印机。
[5] Similar in technology to a photocopier，...: similar to...: 与……类似或相似；类似于……。此处由形容词短语做状语，表示原因。
[6] to screen mail：筛选或过滤邮件。
Choose the best answer for each of the following:
A．A modem and a printer.
B．A modem and a telephone.
C．A modem and a FAX machine.
D．A telephone and a FAX machine.
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