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计算机病毒具有传播性、隐蔽性、感染性、潜伏性、可激发性、表现性或破坏性。接下来小编为大家整理了计算机病毒的介绍,希望对你有帮助哦!
The computer virus is an outcome of the computer overgrowth in the 1980s. The cause of the term "computer virus" is the likeness between the biological virus and the evil program infected with computers. The origin of this term came from an American science fiction“The Adolescence of P-1”written by Thomas J. Ryan, published in 1977. Human viruses invade a living cell and turn it into a factory for manufacturing viruses. However, computer virusesare small programs. They replicate by attaching a copy of themselves to another program.
Once attached to me host Program, the viruses then look for other programs to "infect". In this way, he virus can spread quickly throughout a hard disk or an entire organization when it infects a LAN or a multi-user system. At some point, determined by how the virus was programmed the virus attacks. The timing of the attack can be linked to a number of situations, including a certain time or date, the presence of a particular file, the security privilege level of the user, and the number of times a file is used. Likewise, the mode of attack varies. So-called "benign" viruses might simply display a message, like the one that infected IBM's main computer system last Christmas with a season's greeting. Malignant viruses are designed to damage the system. The attack is to wipe out data, to delete flies, or to format the hard disk.
What Kind of Viruses Are There? There are four main types of viruses: shell, intrusive, operating system and source ode. Shell viruses wrap themselves around a host program and don't modify the original program. Shell programs are easy to write, which is why about half of viruses are of this type. Intrusive viruses Invade an existing program and actually insert a portion of themselves into the host program. Intrusive viruses are hard to write and very difficult to remove without damaging the host file.
计算机病毒是八十年代计算机飞速发展带来的结果,计算机病毒这一名词起因于在计算机上传染的有害程序与生物学中病毒的相似性,该名词起源于1977年出版的、由 Thomas J. Ryan写的一本美国科幻小说《p-1的青春》。人体病毒入侵活的细胞后,就把它转变成制造病毒的工厂。而计算机病毒是一些小程序,它们把自己的一个副本附加到另一个程序上面进行复制。
病毒程序一旦附加到一个主程序上,就开始寻找其他可以进行“感染”的程序。这样,病毒就很快地布满整个硬盘,如果病毒感染了一个局域网或者一个多用户系统,那么就在整个组织内进行扩散。只有在某个点上病毒程序才会发作(这是由病毒程序的设计所决定的)。攻击的时间与多种情况有关,包括:某个时间或日期、特定用户识别符的出现、用户的安全保密等级和一个文件使用的次数。同样,攻击的方式也是各种各样的。所谓的“良性”病毒可能只是简单地显示一个消息,如在去年圣诞节时,受感染的IBM公司的主要计算机系统显示节日问候。恶性病毒被设计出来破坏系统。常见的攻击方式是消除数据、删除文件或者格式化硬盘。
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写作是评价学生综合语言运用能力的重要方面,新课标指出,写作教学的目的是通过对学生进行激活灵感,激发兴趣,整理思路,组织素材,规划结构,遣词造句等基本写作技能的培养,使他们能表达事实、观点、情感和想象力,能交流信息,能形成规范的写作习惯。近年来,中高考对学生的写作要求越来越高,除了要求语法、拼写、句子正确以外,对内容也提出了较高的要求,不但要求文章内容充实,句子通顺连贯,中心突出,还要求使用的句子结构多样化,句子优美、词汇丰富、贴切以及内容上的创新和想象力的发挥。
说明文不同于一般的文学作品,它不需要环境、心境的描写,不需要引人入胜的气氛渲染。说明文的第一个句子就可以直奔主题。如通过Water is veryimportant for living things.一句可以让我们清晰地了解到,该文要说明“水”的重要性。但如果以下述方法作为该文的开头就不符合说明文的要求了:
After I played football with my friends yesterdayafternoon,I was very thirsty. But I couldn’t find anyboiled water to drink. Only then did I realize thathow important water is.
当然,说明文也可以以书信、便条、日记、口头介绍等形式出现。这时,我们应该注意书信等开头的写作格式。如:
I’m glad to get your letter. In your letter,youask me about the importance of water. Now I’ll talkabout it.
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