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Hardware System of Computer(计算机硬件系统)

已有 3528 次阅读2009-1-5 17:50 |个人分类:Computer

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Computer hardware has four parts: the central processing unit (CPU) and memory, storage hardware, input hardware, and output hardware.

  The part of the computer that runs the program is known as the processor or central processing unit (CPU). In a microcomputer, the CPU is on a single electronic component, the microprocessor chip, within the system unit or system cabinet. The CPU itself has two parts: the control unit and the arithmetic-logic unit. In a microcomputer, these are both on the microcomputer chip.

  The Control Unit The control unit tells the rest of the computer system how to carry out a program's instructions. It directs the movement of electronic signals between memory and the arithmetic-logic unit. It also directs these control signals between the CPU and input and output devices.

  The Arithmetic-Logic Unit The arithmetic-logic unit, usually called the ALU, performs two types of operations—arithmetic and logical. Arithmetic operations are, as you might expect, the fundamental math operations: addition, subtraction, multiplication, and division. Logical operations consist of comparisons. That is , two pieces of data are compared to see whether one is equal to, less than, or greater than the other.

  Memory Memory is also known as primary storage, internal storage, it temporarily holds data, program instructions, and information. One of the most important facts to know about memory is that part of its content is held only temporarily. In other words, it is stored only as long as the computer is turned on. When you turn the machine off, the content immediately vanish. The stored contents in memory are volatile and can vanish very quickly.
 Storage Hardware The purpose of storage hardware is to provide a means of storing computer instructions and data in a form. that is relatively permanent, that is, the data is not lost when the power is turned off—and easy to retrieve when needed for processing.There are four kinds of storage hardware: floppy disks, hard disks, optical disk, and magnetic tape.

  Floppy Disks Floppy disks are also called diskettes, flexible disks, floppies, or simply disks. The plastic disk inside the diskette cover is flexible, not rigid. They are flat, circular pieces of mylar plastic that rotate within a jacket. Data and programs are stored as electromagnetic charges on a metal oxide film coating the mylar plastic.

  Hard Disks Hard disks consist of metallic rather than plastic platters. They are tightly sealed to prevent any foreign matter from getting inside. Hard disks are extremely sensitive instruments. The read-write head rides on a cushion of air about 0.000001 inch thick. It is so thin that a smoke particle, fingerprint, dust, or human hair could cause what is known as a head crash. A head crash happens when the surface of the read-write head or particles on its surface contact the magnetic disk surface. A head crash is a disaster for a hard disk. It means that some or all of the data on the disk is destroyed. Hard disks are assembled under sterile conditions and sealed from impurities within their permanent containers.

  Optical Disks Optical disks are used for storing great quantities of data. An optical disk can hold 650 megabytes of data—the equivalent of hundreds of floppy disks. Moreover, an optical disk makes an immense amount of information available on a microcomputer. In optical-disk technology, a laser beam alters the surface of a plastic or metallic disk to represent data. To read the data, a laser scans these areas and sends the data to a computer chip for conversion.
 Magnetic Tape Magnetic tape is an effective way of making a backup, or duplicate, copy of your programs and data. We mentioned the alarming consequences that can happen if a hard disk suffers a head crash. You will lose some or all of your data or programs. Of course, you can always make copies of your hard-disk files on floppy disks. However, this can be time-consuming and may require many floppy disks. Magnetic tape is sequential access storage and can solve the problem mentioned above.

  Input Hardware Input devices take data and programs people can read or understand and convert them to a form. the computer can process. This is the machine-readable electronic signals of 0s and 1s. Input hardware is of two kinds:

  keyboard entry and direct entry. Keyboard Entry Data is input to the computer through a keyboard that looks like a typewriter keyboard but has additional keys. In this method, the user typically reads from an original document called the source document. The user enters that document by typing on the keyboard.

  Direct Entry Data is made into machine-readable form. as it is entered into the computer, no keyboard is used. Direct entry devices may be categorized into three areas: pointing devices (for example, mouse, touch screen, light pen, digitizer are all pointing devices), scanning devices (for example, image scanner, fax machine, bar-code reader are all scanning devices), and voice-input devices.
 Output Hardware Output devices convert machine-readable information into people-readable form. Common output devices are monitors, printers, plotters, and voice output.

  Monitors Monitors are also called display screen or video display terminals. Most monitors that sit on desks are built in the same way as television sets, these are called cathode-ray tubes. Another type of monitor is flat-panel display, including liquid-crystal display (LCD), electroluminescent (EL) display and gas-plasma display. An LCD does not emit light of its own. Rather, it consists of crystal molecules.An electric field causes the molecules to line up in a way that alters their optical properties. Unfortunately, many LCDs are difficult to read in sunlight or other strong light. A gas-plasma display is the best type of flat screen. Like a neon light bulb, the plasma display uses a gas that emits light in the presence of an electric current.

  Printers There are four popular kinds of printers: dot-matrix, laser, ink-jet, and thermal. Dot-Matrix Printer Dot-matrix printers can produce a page of text in less than 10 seconds and are highly reliable. They form. characters or images using a series of small pins on a print head. The pins strike an inked ribbon and create an image on paper. Printers are available with print heads of 9, 18, or 24 pins. One disadvantage of this type of printer is noise.

  Laser Printer The laser printer creates dotlike images on a drum, using a laser beam light source.The characters are treated with a magnetically charged inklike toner and then are transferred from drum to paper. A heat process is used to make the characters adhere. The laser printer produces images with excellent letter and graphics quality. Ink-Jet Printer An ink-jet printer sprays small droplets of ink at high speed onto the surface of the paper. This process not only produces a letter-quality image but also permits printing to be done in a variety of colors.
 Thermal Printer A thermal printer uses heat elements to produce images on heat-sensitive paper. Color thermal printers are not as popular because of their cost and the requirement of specifically treated paper. They are a more special use printer that produces near photographic output. They are widely used in professional art and design work where very high quality color is essential.

  Plotters Plotters are special-purpose output devices for producing bar charts, maps, architectural drawings, and even three-dimensional illustrations. Plotters can produce high-quality multicolor documents and also documents that are larger in size than most printers can handle. There are four types of plotters: pen, ink-jet, electrostatic, and direct imaging.

  Voice-Output Devices Voice-output devices make sounds that resemble human speech but actually are pre-recorded vocalized sounds. Voice output is used as a reinforcement tool for learning, such as to help students study a foreign language. It is used in many supermarkets at the checkout counter to confirm purchases. Of course, one of the most powerful capabilities is to assist the physically challenged.
  计算机硬件具有四部分:中央处理器和内存、存储硬件、输入硬件和输出硬件。

  计算机运行程序的部分被称为处理器或中央处理单元。在微型计算机中,CPU是在一个单独的电子元件上,即微处理器芯片上,它在系统单元内或系统机箱内。CPU本身具有两个部分:控制单元和算术—逻辑单元。在微型计算机中,这两个部分都在微型机芯片上。

  控制单元 控制单元告诉计算机系统的其他部分如何完成程序指令。它指导着内在和算术—逻辑单元之间的电子信息的移动。它也指挥着CPU和输入输出设备之间的控制信号。

  算术—逻辑单元 算术—逻辑单元,通常被称为ALU,完成两类运算——算术和逻辑。自述运算,如你所期望的,是基本的数学运算:加、减、乘、除。逻辑运算是由比较(运算)构成的。也就是说,用数据的两部分进行比较,以看其中一个是否是等于、小于或大于另一个。

  内存 内存也被称为主存储器、内部存储器,它临时地存储数据、程序指令和信息。对于内存需要了解的一个最重要的事实是它所保存的内容只是临时的。换句话说,它只在计算机开着时才保存(数据)。当机器被关闭时,其内容会立即消失。在内存中所存储的信息是易指令性的并能很快消失。
 存储硬件 存储硬件的作用是以一种相对持久的形式提供存储计算机指令和数据的方法,即当切断电源时数据不会丢失——且当需要处理数据时又容易恢复。存储硬件有四种:软盘、硬盘、光盘和磁带。

  软盘 软盘又被称为软磁盘、可弯曲磁盘、软盘、或简单地称为磁盘。在磁盘表面内部的塑料盘是柔软的,不是坚硬的。这些塑料盘是平的、在一个套子内部旋转的圆的聚脂塑料片。程序和数据是以电磁荷的形式存储在聚脂塑料外面包着的金属氧化胶片上。

  硬盘 硬盘是由金属盘片而不是塑料盘片组成的。它们被紧紧地密封起来,以防止外界东西进入。硬盘是非常灵敏的设备。读写头浮在大约0.000001英寸厚的空气气垫上。它是如此的薄,以至于烟粒、指印、灰尘或者头发都可能引起磁头划伤。当读写头的表面或表面上的微粒与磁盘表面接触时会发生磁头划伤。磁头划伤对于硬盘来讲是灾难,它意味着磁盘上的数据部分或全部丢失。硬盘是在无菌条件下安装并且密封在远离杂质的永久的容器内。

  光盘 光盘用于存储大量的数据。一个光盘可能容纳650兆字节的数据——相当于数以百计的软盘。并且,光盘使用大量的信息用于微机上。在光盘技术中,激光束改变塑料或金属盘的表面来代表数据。为了记取数据,激光扫描这些区域并且将这些数据送给计算机芯片以转换。

  磁带 磁带是备份,即复制、拷贝程序和数据的有效方法。我们曾提到如果硬盘遭遇磁头划伤就会产生令人担忧的结果,你将会丢失部分或全部的程序或数据。当然,你可以将硬盘上的文件拷贝到软盘上。然而这很耗时,并且需要很多软盘。磁带是顺序访问存储,能够解决上面所提问题。
 输入硬件 输入硬件接收人们能读懂的程序和数据并将其转换为计算机能处理的形式。这就是机器可读的电子信号0和1。有两种输入硬件:键盘输入和直接输入。

  键盘输入: 数据通过形似打字机键盘但有附加键的键盘输入到计算机。用这种方式,用户一般读取被称为是源文件的初始文件。用户通过在键盘上打字而输入那个文件。

  直接输入:当数据输入到计算机时,是以机器可读懂的形式输入的,不需要键盘。直接输入设备可以被分成三类:指针设备(如:鼠标、触摸屏、光笔、数字化仪都是指针设备)、扫描设备(如图像扫描仪、传真机、条形码读器都是扫描设备)和声音输入设备。

  输出硬件 输出设备将机器可读的信息转换为人类可读的形式。一般的输出设备有监视器、打印机、绘图仪和声音输出设备。

  监视器 监视器也被为屏幕显示或视频显示终端。大多数放在桌面上的监视器的制作方法同电视一样,被称为是阴极射线管。另一类的监视器是平板显示器,包括液晶显示、光电发光显示和等离子显示。液晶显示自己不发射光,相反,是由晶体分子组成,电场使得这些分子排成一行,在某种程度上改变着它们的光学特性。不幸的是,许多液晶显示器在太阳光或其他强光下很难读到。等离子显示器是平板显示器中最好的一种,像霓光灯泡,等离子显示器在电流存在的情况下使用一种发光的气体。

 输入硬件 输入硬件接收人们能读懂的程序和数据并将其转换为计算机能处理的形式。这就是机器可读的电子信号0和1。有两种输入硬件:键盘输入和直接输入。

  键盘输入: 数据通过形似打字机键盘但有附加键的键盘输入到计算机。用这种方式,用户一般读取被称为是源文件的初始文件。用户通过在键盘上打字而输入那个文件。

  直接输入:当数据输入到计算机时,是以机器可读懂的形式输入的,不需要键盘。直接输入设备可以被分成三类:指针设备(如:鼠标、触摸屏、光笔、数字化仪都是指针设备)、扫描设备(如图像扫描仪、传真机、条形码读器都是扫描设备)和声音输入设备。

  输出硬件 输出设备将机器可读的信息转换为人类可读的形式。一般的输出设备有监视器、打印机、绘图仪和声音输出设备。

  监视器 监视器也被为屏幕显示或视频显示终端。大多数放在桌面上的监视器的制作方法同电视一样,被称为是阴极射线管。另一类的监视器是平板显示器,包括液晶显示、光电发光显示和等离子显示。液晶显示自己不发射光,相反,是由晶体分子组成,电场使得这些分子排成一行,在某种程度上改变着它们的光学特性。不幸的是,许多液晶显示器在太阳光或其他强光下很难读到。等离子显示器是平板显示器中最好的一种,像霓光灯泡,等离子显示器在电流存在的情况下使用一种发光的气体。


 打印机 有四种流行的打印机:点阵式、激光式、喷墨式和热敏式。

  点阵式打印机 能在不到几秒的时间内打印一页文本并且非常可靠。点阵式打印机利用在打印头上的一系列小针来形成字符或图像。这些针击打喷墨的色带并在纸上产生图像。有9针、18针和24针的打印机,这种打印机的一个缺点是它的噪音。

  激光打印机 使用激光光束光源在磁鼓上产生小点一样的图像,用磁化的带电的像墨一样的碳粉处理这些字符,然后从磁鼓传送到纸上。这一过程不仅印刷高质量的图像,并且能打印彩色图像。

  热敏式打印机 全用热元素在热感应纸上产生图像。由于价格以及需要特殊处理的纸张,彩色热敏打印机不是很普及。热敏式打打印机是打印逼真输出的特殊打印机。它们被广泛应用在要求高质量彩色输出的专业艺术设计工作中。

  绘图仪 是特殊用途的输出设备,用于产生条形图、地图、建筑绘图、甚至三维图表。绘图仪可以输出高质量的多种色彩的文档,并且文档的尺寸比大多数打印机能处理的要大。有四种类型的绘图仪:钢笔、喷墨、静电和直接图像。

  声音输出设备 声音输出设备可以发出类似于人类说话的声音,但实际上是事先录制的声音。声音输出被用作学习的加强工具,例如帮助学生学习外语。它被用于许多超市的检验柜来确认购买。当然,它最强大的功能是用来帮助残障者。


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