外文翻譯computerprogram英文

1、Computer Program1 IntroductionComputer Program, set of instructions that directs a computer to perform somep rocessing function or combination of functions. For the instructions to be carried out, a computer must execute a program, that is, the computer reads the program, and then follow the steps e

2、ncoded in the program in a precise order until completion. A program can be executed many different times, with each execution yielding a potentially different result depending upon the options and data that the user gives the computer.Programs fall into two major classes: application programs and o

3、perating systems. An application program is one that carries out some function directly for a user, such as word processing or game-playing. An operating system is a program that manages the computer and the various resources and devices connected to it, such as RAM,h ard drives, monitors, keyboards

4、, printers, and modems,s o that they mayb e used by other programs. Examples of operating systems are DOS, Windows 95, OS2, and UNIX.2 Program DevelopmentSoftware designers create new programs by using special applications programs, often called utility programs or development programs. A programmer

5、 uses another type of program called a text editor to write the new program in a special notation called a programming language. With the text editor, the programmer creates a text file, which is an ordered list of instructions, also called the program source file. The individual instructions that m

6、ake up the program source file are called source code. At this point, a special applications program translates the source code into machine language, or object code a format that the operating system will recognize as a proper program and be able to execute.Three types of applications programs tran

7、slate from source code to object code: compilers, interpreters, and assemblers. The three operate differently and on different types of programming languages, but they serve the same purpose of translating from a programming language into machine language.A compiler translates text files written in

8、a high-level programming language-such as FORTRAN, C,o r Pascal from the source code to the object code all at once. This differs from the approach taken by interpreted languages such as BASIC, APL and LISP, in which a program is translated into object code statement by statement as each instruction

9、 is executed. The advantage to interpreted languages is that they can beginexecuting the program immediately instead of having to wait for all of the source code to be compiled. Changes can also be made to the program fairly quicklywithout having to wait for it tobe compiled again. The disadvantage

10、of interpreted languages is that they are slow to execute, since the entire program must be translated one instruction at a time, each time the program is run. On the other hand, compiled languages are compiled only once and thus can be executed by the computer much more quickly than interpreted lan

11、guages. For this reason, compiled languages are more common and are almost always used in professional and scientific applications.Another type of translator is the assembler, which is used for programs or parts of programs written in assembly language.Assembly language is another programming langua

12、ge, but it is much more similar to machine language than other types of high-level languages. In assembly language, a single statement can usually be translated into a single instruction of machine language. Today, assembly language is rarely used to write an entire program, but is instead most ofte

13、n used when the programmer needs to directly control some aspect of the computer s function.Programs are often written as a set of smaller pieces, with each piece representing some aspect of the overall application program. After each piece has been compiled separately, a program called a linker com

14、bines all of the translated pieces into a single executable program.Programs seldom work correctly the first time, so a program called a debugger is often used to help find problems called bugs. Debugging programs usually detect an event in the executing program and point the programmer back to the

15、origin of the event in the program code.Recent programming systems, such as Java, use a combination of approaches to create and execute programs. A compiler takes a Java source program and translates it into an intermediate form. Such intermediate programs are then transferred over the Internet into

16、 computers where an interpreter program then executes the intermediate form as an application program.3 Program ElementsMost programs are built from just a few kinds of steps that are repeated many times in different contexts and in different combinations throughout the program. The most common step

17、 performs some computation, and then proceeds to the next step in the program, in the order specified by the programmer.Programs often need to repeat a short series of steps many times, for instance in lookingthrough a list of game scores andfinding the highest score. Such repetitive sequences of co

18、de are called loops.One of the capabilities that makes computer so useful is their ability to make conditional decisions and perform different instructions based on the values of data being processed. If-then-else statements implement this function by testing some piece of data and then selecting on

19、e of two sequences of instructions on the basis of the result. One of the instructions in these alternatives may be a goto statement that directs the computer to select its next instruction from a different part of the program. For example, a program might compare two numbers and branch to a differe

20、nt part of the program depending on the result of the comparison:If x is greater than yThenGoto instruction # 10Else continueProgram often use a specific sequence of steps more than once. Such a sequence of steps can be grouped together into a subroutine, which can then be called, or accessed, as ne

21、ededin different parts of the main program. Each time a subroutine is called, the computer remembers where it was in the program when the call was made, so that it can return there upon completion of the subroutine, allowing a very general piece of code to be written once and used in multiple ways.M

22、ost programs use several varieties of subroutines. The most common of these are functions, procedures, library routines, system routines, and device drivers. Functions are short subroutines that compute some value, such as computations of angles, which the computer cannot compute with a single basic

23、 instruction. Procedures perform amore complex function, suchas sorting a set of names. Library routines are subroutines that are written for use by many different programs. System routines are similar to library routines but are actually found in the operating system. They provide somes ervice for

24、the application programs, such as printing a line of text. Device drivers are system routines that are added to an operating system to allow the computer to communicate with a new device, such as a scanner, modem,o r printer. Device drivers often have features that can be executed directly as applic

25、ations programs. This allows the user to directly control the device, which is useful if, for instance, a color printer needs to be realigned to attain thebest printing quality after changing an ink cartridge.4 Program FunctionModern computers usually store programs on some form of magnetic storage

26、media that can be accessed randomly by the computer, such as the hard drive disk permanently located in the computer, or a portable floppy disk. Additional information on such disks, called directories, indicate the names of the various program begins on the disk media. When a user directs the compu

27、ter to execute a particular application program, the operating system looks through these directories, locates the program, and reads a copy into RAM. The operating system then directs the CPU to start executing the instructions at the beginning of the program. Instructions at the beginning of the p

28、rogram prepare the computer to process information by locating free memory locations in RAM to hold working data, retrieving copies of the standard options and defaults the user has indicated from a disk, and drawing initial displays on the monitor.The application program requests copy of any inform

29、ation the user enters by making a call to a system routine. The operating system converts any data so entered into a standard internal form. The application then uses this information to decide whatto do next-forexample, perform some desired processing function such as reformatting a page of text, o

30、r obtain some additional information from another file on a disk. In either case, calls to other system routines are used to actually carry out the display of the results or the accessing of the file from the disk.Whent he application reaches completion or is prompted to quit, it makes further syste

31、m calls to make sure that all data that needs to be saved has been written back to disk. It then makes a final system call to the operating system indicating that it is finished. The operating system then frees up the RAMa nd any device that the application was using and awaits a commandfr om the us

32、er to start another program.5 HistoryPeople have been storing sequences of instructions in the form of a program for several centuries. Music boxes of the 18 th century and player pianos of the late 19th and early 20th centuries played musical programs stored as series if metal pins, or holes in pap

33、er, with each line representing when a note was to be played, and the pin or hole indicating what note was to be played at that time. More elaborate control of physical devices became common in the early 1800s with French inventorJoseph Marie Jacquard s invention of the punch-card controlled weaving

34、 loom. In the process of weaving a particular pattern, various parts of the loom had to be mechanically positioned. To automate this process, Jacquard used a single paper card to represent each positioning of the loom, with hole in the card to indicate which loom actions should be done. An entire ta

35、pestry could be encoded onto a deck of such cards, with the same deck yielding the same tapestry design each time it was used. Programs of over 24,000 card were developed and used.The world s firstprogrammablemachine wasThis machine,called the AnalyticalEngine, used punch cards similarto thosedesign

36、ed-althoughnever fullybuilt-bythe English mathematician and inventor, Charles Babbage.used in the Jacquard loom to select the specific arithmetic operation to apply at each step. Inserting a different set of cards changed the computations the machine performed. This machine had counterparts for almo

37、st everything found in modern computers, although it was mechanical rather than electrical. Construction of the Analytical Engine was never completed because the technology required to build it did not exist at the time.The first card deck programs for the Analytical Engine weredeveloped by British

38、mathematician Countess Augusta Ada Lovelace, daughter of the poet Lord Byron. For this reason she is recognized as the world s first programmer.The modern concept of an internally stored computer program was first proposed by Hungarian-American mathematician John von Neumannin 1945. Von Neumann s id

39、ea was to use the computer s memory to store the program as well as the data. In this way, programs can be viewed as data and can be processed like data by other programs. This idea greatly simplifies the role of program storage and execution in computers.6 The FutureThe field of computer science ha

40、s grown rapidly since the 1950s due to the increase in their use. Computer programs have undergone manyc hanges during this time in response to user need and advances in technology. Newer ideas in computing such as parallel computing, distributed computing, and artificial intelligence, have radicall

41、y altered the traditional concepts that once determined program form and function.Computer scientists working in the field of parallel computing, in which multiple CPUsc ooperate on the samep roblem at the same time, have introduced a number of new program models. In parallel computing parts of a problem are worked on simultaneously by different processors, and this speeds up the solution of the problem. Many challenges face