five categories of computer hardware

  1. Input
  2. Storage
  3. Data Processing and Memory(primary storage主存,working storage,Random access memory,is temporary working storage.) Memory is the computer's "work area",where data and programs needed for immediate processing are held.
  4. Communications
  5. Output

Peripheral devices

  1. Devices that are connected to the computer and controlled by the computer are referred to as peripheral devices.These devices can be external,such ad keyboards,mice,monitors,and printers,or they can be internal(inside the coumputer cabinet),such as a floppy disk driver.
  2. Secondary storage hardware serves the same basic functions as do office filing systems except that it stores data as eletromagnetic signals or laser-etched spots,commonly on magnetic disk,optical disk,or tape,rather than on paper.
  3. Output hardware:for example,previously input but unorganized sales figures may be processed into meaningful form and displayed on a computer screen(softcopy) or printed out on paper(hardcopy).

computer software

  1. A computer has no intelligence of own and must be supplied with instructions that tell it what to do and how and when to do it.These instructions are called software,because you can't feel it or see it.It flows through the computer's circuits as coded pulses of electricity.
  2. Software is made up of a group of related programs written in a specific code called a programming and based on the computer's language of 0s and 1s.
  3. Software designed to allow the computer to manage its own resources and run the hardware and basic operations is called system software.System software consists of programs to control the operations of computer equipment.An important part of system software is set of programs called operating system.Instructions in the operating system tell the computer how to perform the functions of loading,storing,and executing an application program and how to transfer data.For a computer is turned on,the operating system is loaded into the computer's memory from anxiliary storage.This process is called booting.
  4. Today,most computers use an operating system that has a graphical user interface(GUI)that provides visual cues such as icon symbols to help the user.Each icon represents and application such as word processing,or a file or document where data is stored.A icon represents a program,an instruction,or some other objects the user can choose.A window is a rectangular area of the screen that is used to display a program,data,and/or information.

Language and its translator

  1. Ultimately,programs written in a particular language must be reduced to digital for 1s or 0s,because that is all the computer can understand.
  2. Because a computer can execute programs only in machine language,a translator or converter is needed if the program is written in any other language.A language translator is a type of system software that translates a program wirtten in a second-or higher-generation lanuage into machine languages.
  3. 因为计算机只能以机器语言的形式运行程序。如果程序是用另一种语句编写的，则需要一个翻译器或转换器。语言翻译器是一种系统软件，它能够将第二代或更高一代语言写的程序翻译成机器语言。
  4. Language translators are three types:(1) Assemblers,(2) Compilers,(3) Interpreters.
  5. 语言翻译器有三种类型：汇编程序、编译程序、解释程序；
  6. An assembler,or,assemble program,is a program that translates the assembly language program into machine language.
  7. 汇编程序是将汇编语言程序翻译成机器语言的程序。
  8. A high-level language is an English-like language,such as COBOL and BASIC.Such languages allow users to wirte in a familiar notation,rather than numbers or abbreviations.Most high-level languages are not machine dependent -then can be used on more than one kind of computer.
  9. 高级语言是类似于英语的语言，如COBOL和BASIC。这样的放言允许用户用熟悉的记号而不是用数字或缩写来写程序。大多数高级语言是不依赖于机器的－它们能在多种类型的计算机上使用。
  10. As we mentioned,assembly language requires an assembler as a language translator.The translator for high-level language is,depending on the language,either a compiler or an interpreter.
  11. A compiler is software that looks at an entire high-level program before translating it into machine language.The programming instructions of a high-level language are called source code.The compiler translates source code into machine language,which in this case is called the object code.With compiler,the object code can be saved and run later.That is,the object code doesn't have to be recompiled.As a result,compiled programs run faster than interpreted programs.
  12. 编译器是一种在将高级语言程序翻译成机器语言之前阅读整个程序的软件。高级语言的程序指令称为源代码。编译器将源翻译为机器语言，这样的代码称为目标代码。使用编译器，目标代码可以存储并且可以以后执行。也就是说，目标代码不必重新编译。因此编译程序比解释程序运行更快。
  13. Examples of high-level languages using compilers are C and COBOL.
  14. An interpreter is software that converts high-level language statements into machine language one at a time,in succession.Unlike compilers,which must look at an entire program before converting it into machine language,interpreters,provide programmmers with immediate feedback regarding the accuracy of their coded instructions.However,as mentioned previously,a program that must be interpreted runs more slowly than a compiled program.Interpreters are sometimes used by programmers when developing a program and in education to allow student to program interactively.
  15. 解释器是一种将高级语言逐条转换为机器代码且重复进行的软件。不像编译器，必须在转换成机器语言之前阅读整个程序，解释器对程序员的指令代码的准确性提供即时的反馈。然而，如前所述，一个需要解释的程序比编译的程序运行速度慢。当开发程序和在教学中允许学生互动编程的时候，程序员有时使用解释器。
  16. Examples of high-level language that use an interpreter are BASIC and LISP.

Operating Systems

  1. The OS is iteslf a program.Which is written,compiled,tested and debugged just like any other program.It is certainly larger than anything the average student has written so far.This program is run whenever a computer is switched on.It is almost always done automatically,no special command is required.So users may not be aware that it happens every time they switch on a machine.It stays running until the machine is switched off.

Binary coding scheme

  1. Electricity can be either on or off.Other kinds of technology also use this two-state on/off arrangement.An electrical circuit may be open or close.The magnetic pulses on a disk or tape may be present or absent.Curren may be high voltage or low voltage.A punched card or tape may have a hole or not have a hole.The two-state situation allows computer to use the binary system represent data and programs.
  2. The decimal system that we are accustomed to has 10 digits.By contrast,the binary system has only two digits:0,1.Thus ,in the computer by the 0 and 1 can be represented the electrical current being off(or at low voltage) and 1 by the current being on(or at high voltage).All data and programs that go into the computer are represented in terms of these numbers.For example,the lettle H is a translation of the electronic signal 01001000,or off-on-off-off-on-off-off-off.When you press the key for H on the computer keyboard,the character id automatically converted into the series of electronic impulses that the computer recognizes.
  3. All the amazing things that computers do are based on binary numbers made up of 0s and 1s.fortunately,we don't have to enter data into the computer using groupsI of 0s and 1s.Instead,we use natural-language characters such as those on the keyboard to input data.Then the computer system encodes the data by means of binary,or digital.Coding schemes to represent letters.numbers and special characters.
  4. There are many coding schemes.Two common ones are EBCDIC and ASCII.Both commonly use 8 bits to form each character,or byte,providing up to 256 combinations with which to form letters,numbers,and special characters,such as math symbols and Greek letters.One newer coding scheme uses 16 bits,enabling it to represent 65535 unique characters.

Database

  1. A database is a collection of many related files.the files are usually integrated,meaning that the file records are logically related,or cross-referenced,to one another.Thus,even though all data elements on a topic are kept in records in different files,they can easily be organized and retrieved with simple requests.
  2. The software for manipulating database is a database management system(DBMS),or database manager,a program that controls the structure of a database and access to the data.
  3. Just as files can be organized in different ways(sequentially or directly,for example),so can databases.The four common arrangements for database management systems are hierarchical,network,relational,and object-oriented.

network

  1. The primary function of the data set(modem) at the transmit end is to convert digital pulses to analog signals suitable for transmission on the PTN and,at the receive end,to convert the analog signals back to digital information.

API Application Programming Interface

  1. From the programmer's point of view,Windows 2000 is defined by the way that a program interacts with it.All application programs communicates with Windows 2000 through a call-based interface.The Windows 2000 call-based interface is an extensive set of system-defined functions that provide access to operating system features.Collectively,these functions are termed the Application Programming Interface.or API for short.The API contains several hundred functions,such as allocating memory,outputting to the screen,creating windows,and the like.These is a subset to the API called the GDI(Graphics Device Interface)that is the part of Windows that provides device-independent graphics support.
  2. There are two basic flavors of the API in common use:Win16 and Win32.The two APIs differ in two fundamental ways.First,Win32 supports 32-bit,flat addressing.Second,Win32 includes API functions that support thread-based multitasking,security,and the other enhanced features that are not available in Win16.
  3. Dynamic Link Libraries(DLLs):The Win32 API functions are contained in Dynamic Link Libraries,or DLLs for short,which each program has access to when it is executed.The API functions are stored in a relocatable format within a DLL.During the complilation phase, when your program calls an API function.the linker does not add the code for that function to the executable version of your program.Instead,it adds loading instructions for tha functions.such as what DLL it resides in and its name.When your program is executed,the necessary API routines are also loaded by the Windows 2000 loader.in this way,each application program does not need to contain the actural API code while store on disk.The code is added only when the program is loaded into memory for execution.
  4. Dynamic linking has some very important benefits.
    First,since virtually all programs will use the API functions,DLLs prevent disk space from being wasted by the significant amount of duplicated object code that would be created if the API functions were actually added to each program's executable file on disk.
    Second,updates and enhancements to Windows 2000 can be accomplished by changing the dynamic link library routines.Existing application program does not need to be recompiled.
    Third,using the dynamic link approach makes the emulation of other operating systems an easier task.

Basic concept of WWW

  1. In 1989 Timothy Berners-lee and other researchs at the CERN research facility neare Geneva,Wsitzerland,laid the foundation of the World Wide Web.They wanted a method that would make it easy for researchers to share data electronically,so they created a system of hypertext documents-electronic files connected by elements known as links.Links are words,phrases,or graphic images that you can select,usually by clicking a mouse,to move to another part of a document or another document altogether.
  2. The system of hypertext document developed at CERN proved to be easily adaptable to other information sources on the Internet.Within a few years,numerous organizations were creating hypertext documents for a large variety of topics.Because linking these different hypertext documents together was easy,a single user could jump from one set of hypertext documents became known as the World Wide Web,or simply the Web.
  3. Each hypertext document on the Web is called a Web page and is stored on a computer on the Internet called a Web server.A web page can contain links to other Web pages located anywhere on the Internet-on the same computer as the original Web page or on an entirely different computer halfway across the world.The ability to cross-reference other Web pages with links is one of the Web's most important features.

What is an internet search engine?

  1. Search engines are the software used to search databases.An Internet search engine is software used to search a database of Internet documents.Each time you use one of these search engines,you are querying a database of Internet documents.Each of these records contains a link to a real document on the Internet.
  2. The biggest differences among search engines are how the database are created.A database can be created either by hand or by automated means.Automatically-created databases will be referred to in this tutorial as robot-generated databases and human created resources as human-selected databases.
  3. Some important points to keep in mind:1 No search engine is perfect;No database is complete;No database is up to date;Search engines often change.

Firewall

  1. A firewall is network access control device that is designed to deny all traffic except that which is explicitly allowed.This definition contrasts with a router,which is a network device that is intended to route traffic as fast as possible.
  2. Some will argue that a router can be a firewall.I will agree that a router can perform some of the functions of a firewall but one key difference remains:a router is intended to route all traffic to flow while a router is a network device that can be configured to deny certain traffic.