外文翻译computerprogram英文.doc

Computer Program1 IntroductionComputer Program, set of instructions that directs a computer to perform someprocessing 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 encoded 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 operating systems. An application program is one that carries out somefunction 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,hard drives, monitors, keyboards, printers, and modems,so that they maybe used by other programs. Examples of operating systems are DOS, Windows 95, OS\2, and UNIX.2 Program DevelopmentSoftware designers create new programs by using special applications programs, often called utility programs or development programs. A programmer 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 make 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 systemwill recognize as a proper program and be able to execute.Three types of applications programs translate 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 samepurpose of translating from a programming language into machine language.A compiler translates text files written in a high-level programming language--such as FORTRAN, C,or 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 is executed. The advantage to interpreted languages is that they can beginexecuting the program immediately instead of having to wait forall of the source code to be compiled. Changes can also be madeto the program fairly quickly without having to wait for it tobe compiled again. The disadvantage of interpretedlanguagesis that they are slow to execute, since the entire program mustbe translated one instruction at a time, each time the programis run. On the other hand, compiled languages are compiled onlyonce and thus can be executed by the computer muchmore quicklythan interpreted languages. For this reason, compiled languages are more common and are almost always used in professional and scientificapplications.Another type of translator is the assembler, which is used forprograms or parts of programs written in assembly language.Assembly language is another programming language,but it ismuch more similar to machine language than other types of high-level languages. In assembly language, a single statementcan usually be translated into a single instruction of machinelanguage. Today, assembly language is rarely used towrite anentire program, but is instead most often used when the programmer needs to directly control some aspect of the computer 'sfunction.Programs are often written as a set of smaller pieces, with eachpiece representing some aspect of the overall application program. After each piece has been compiled separately,program called a linker combines all of thetranslated piecesinto a single executableprogram.Programs seldom work correctly the first time, so aprogramcalled a debugger is often used to help findproblems calledbugs. Debugging programs usually detect an event in the executing program and point the programmer back tothe originof the event in the programcode.Recent programming systems, such as Java, use a combination ofapproaches to create and execute programs. A compiler takes aJava source program and translates it into an intermediate form .Such intermediate programs are then transferred over theInternet into computers where an interpreter program thenexecutes the intermediate form as an applicationprogram.3 Program ElementsMost programs are built from just a few kinds of steps that arerepeated many times in different contexts and indifferentcombinations throughout the program. The most common step performs some computation, and then proceeds to thenext stepin the program, in the order specified by theprogrammer.Programs often need to repeat a short series of steps manytimes,through a list of game scores and for instance in lookingfinding the highest score. Such repetitive sequences of code are called loops.One of the capabilities that makes computer so useful istheir 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 one of two sequences of instructions on the basis of the result. Oneof theinstructions 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 different 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 needed in different parts of the main program. Each time asubroutineis 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.Most 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 ofangles, which the computer cannot compute with a single basic as sorting a set of names. Library routines are subroutines that are written for use by manydifferent programs. System routines are similar to library routines but are actually found in the operating system. They provide someservice for 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,or printer. Device drivers often have features that can be executed directly as applications 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 the best printing quality after changing an ink cartridge.instruction. Procedures perform a more complex function, such 4 Program FunctionModern computers usually store programs on some form of magnetic storage 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 computer 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 executingthe instructions at the beginning of the program.Instructions at the beginning of the program 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 information 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---for example, perform some desired processingfunction such as reformatting a page of text, or obtain some additional information from another file on adisk. In eithercase, calls to other system routines are used to actually carr yout the display of the results or the accessing of the file fromthedisk.Whenthe application reaches completion or is prompted to qui t,it makes further system calls to make sure thatall data thatneeds to be saved has been written back to disk. Itthen makesa final system call to the operating system indicating that itis finished. The operating system then frees up the RAMand anydevice that the application was using and awaits a commandfromthe user to start anotherprogram.5HistoryPeople have been storing sequences of instructions in the formof a program for several centuries. Music boxes of the 18 thcentury and player pianos of the late 19th and early 20thcenturies played musical programs stored as seriesif metalpins, or holes in paper, with each line representing whena notewas to be played, and the pin or hole indicating whatnote wasto be played at that time. More elaborate controlof physicaldevices became common in the early 1800s with French inventorJoseph Marie Jacquard 's invention of the punch-cardcontrolled weaving 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 tapestry could be encoded onto a deck of such cards, with the same deck yielding the same tapestry design each time itwas used. Programs of over 24,000 card were developed and used.The world ' s first programmable machine was designed---although never fully built---by the English mathematician and inventor, Charles Babbage. This machine, called the Analytical Engine, used punch cards similar to those 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 almost 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 were developed by British mathematician Countess Augusta AdaLovelace, daughter of the poet Lord Byron. For this reason sheis recognized as the world ' s firstprogrammer.The modern concept of an internally stored computer program wasfirst proposed by Hungarian-American mathematicianJohn vonNeumannin 1945. Von Neuman'n s idea was to use the computer ' smemory to store the program as well as the data. Inthis way,programs can be viewed as data and can be processedlike databy other programs. This idea greatly simplifiesthe role ofprogram storage and execution incomputers.6 The FutureThe field of computer science has grown rapidly since the 1950sdue to the increase in their use. Computer programs have undergone manychanges during this time in response to user needand advances in technology. Newer ideas in computingsuch asparallel computing, distributed computing, and artificial intelligence, have radically altered thetraditionalconcepts that once determined program form andfunction.Computer scientists working in the field of parallel computing ,in which multiple CPUscooperate on the sameproblem at the sametime, have introduced a number of new program models. In parallel computing parts of a problem are worked onsimultaneously by different processors, and this speeds upthesolution of the problem. Many challenges facescientists andengineers who design programs for parallel processingcomputers, because of the extreme complexity of the systems andthe difficulty involved in making them operate as effectivelyaspossible.Another type of parallel computing called distributed computing uses CPUsfrom manyinterconnected computers to solve problems. Often the computers used to processinformation ina distributed computing application are connectedover theInternet. Internet applications are becoming aparticularlyuseful form of distributed computing, especially with programming languages such as Java. In suchapplications, auser logs onto a website and downloads a Java program onto thei rcomputer. When the Java program is run, itcommunicates withother programs at its home Web site, and may also communicatewith other programs running on different computers or Web sites.Research into artificial intelligence has led to several othernew styles of programming. Logic programs, for example, do notconsist of individual instructions for thecomputer to followblindly, but instead consist of sets of rules: if x happens thendo y. A special program called an inference engineuses theserules to “reason ” its way to a conclusion whenpresented with a newproblem. Applications of logic programs include automatic monitoring of complex systems, and proving mathematical theorems.A radically different approach to computing in which there is no program in the conventional sense is called a neural network.A neural network is a group of highly interconnected simple processing elements, designed to mimic the brain. Instead of having a program direct the information processing in the way that a traditional computer does, a neural network processes information depending upon the waythat its processing elements are connected. Programming a neural network is accomplished by presenting it with known patterns of input and output data and adjusting the relative importance of the interconnections between the processing elements until the desired pattern matching is accomplished. Neural networks are usually simulated on traditional computers, but unlike traditional computer programs, neural networks are able to learn from their experience.。